Display device and driving method of display device

ABSTRACT

A display device that can switch between normal display and see-through display is provided. Visibility in see-through display is improved. A liquid crystal element overlaps with a light-emitting element. The light-emitting element, a transistor, and the like overlapping with the liquid crystal element transmit visible light. When the liquid crystal element blocks external light, an image is displayed with the light-emitting element. When the liquid crystal element transmits external light, an image displayed with the light-emitting element is superimposed on a transmission image through the liquid crystal element.

TECHNICAL FIELD

One embodiment of the present invention relates to a display device, amanufacturing method of the display device, and a driving method of thedisplay device.

Note that one embodiment of the present invention is not limited to theabove technical field. Examples of the technical field of one embodimentof the present invention disclosed in this specification and the likeinclude a semiconductor device, a display device, a light-emittingdevice, a power storage device, a memory device, an electronic device, alighting device, an input device, an input/output device, a drivingmethod thereof, and a manufacturing method thereof.

In this specification and the like, a semiconductor device generallymeans a device that can function by utilizing semiconductorcharacteristics. A transistor, a semiconductor circuit, an arithmeticdevice, a memory device, and the like are each an embodiment of thesemiconductor device. In addition, an imaging device, an electro-opticaldevice, a power generation device (e.g., a thin film solar cell and anorganic thin film solar cell), and an electronic device each may includea semiconductor device.

BACKGROUND ART

In recent years, the diversification of display devices has beenrequired. A variety of possible display devices includes a displaydevice having a see-through capability. The display device has alight-transmitting display portion through which the background behindthe display portion can be seen. Expectative applications of such asee-through display device are, for example, windshields of vehicles;windows of architectural structures such as houses and buildings; glassfor show windows or showcases of stores; information terminal devicessuch as cellular phones and tablet terminals; wearable displays such ashead mounted displays; and head-up displays used for cars and planes.

Display devices using organic electroluminescent (EL) elements or liquidcrystal elements have been known. Examples of the display device alsoinclude a light-emitting device provided with a light-emitting elementsuch as a light-emitting diode (LED), and electronic paper performingdisplay with an electrophoretic method or the like.

The organic EL element generally has a structure in which a layercontaining a light-emitting organic compound is provided between a pairof electrodes. By voltage application to this element, thelight-emitting organic compound can emit light. A display deviceincluding such an organic EL element can be thin and lightweight andhave high contrast and low power consumption.

An active matrix liquid crystal display device, in which a transistorwhose channel formation region includes a metal oxide is used as aswitching element connected to a pixel electrode, has been known (seePatent Document 1 and Patent Document 2).

REFERENCE Patent Document [Patent Document 1] Japanese Published PatentApplication No. 2007-123861 [Patent Document 2] Japanese PublishedPatent Application No. 2007-096055 DISCLOSURE OF INVENTION

Various image display techniques such as virtual reality (VR) oraugmented reality (AR) have been actively developed in recent years.Thus, a display device is required to have various functions in additionto a simple function of displaying an image.

An object of one embodiment of the present invention is to provide adisplay device that can switch display methods. Another object is toimprove visibility in see-through display. Another object is to providea display device that can switch between normal display and see-throughdisplay. Another object is to provide a display device that offers highuser safety.

Another object is to provide a novel display device or a driving methodof the novel display device. Another object is to provide a highlyreliable display device. Another object is to provide a lightweightdisplay device. Another object is to provide a thin display device.

Note that the descriptions of these objects do not disturb the existenceof other objects. In one embodiment of the present invention, there isno need to achieve all the objects. Note that other objects can bederived from the description of the specification, the drawings, theclaims, and the like.

One embodiment of the present invention is a display device including alight-emitting element, a liquid crystal element, and a firsttransistor. The first transistor is electrically connected to thelight-emitting element, and includes a first gate electrode, a firstsemiconductor layer, a first source electrode, and a first drainelectrode. At least one of the first gate electrode, the firstsemiconductor layer, the first source electrode, and the first drainelectrode has a function of transmitting visible light. The liquidcrystal element overlaps with the first transistor. The liquid crystalelement transmits light when applied with an electric field, and blockslight when applied with no electric field.

In the above embodiment, the light-emitting element preferably includesa first electrode, a second electrode, and a light-emitting layerbetween the first electrode and the second electrode. The firstelectrode and the second electrode each preferably have a function oftransmitting visible light.

In the above embodiment, at least one of the first semiconductor layer,the first gate electrode, the first source electrode, and the firstdrain electrode preferably includes a metal oxide.

In the above embodiment, the display device preferably includes a secondtransistor electrically connected to and overlapping with the liquidcrystal element. The second transistor preferably includes a second gateelectrode, a second semiconductor layer, a second source electrode, anda second drain electrode. At least one of the second gate electrode, thesecond semiconductor layer, the second source electrode, and the seconddrain electrode preferably has a function of transmitting visible light.

In the above embodiment, the first transistor and the second transistorare preferably on the same plane.

In the above embodiment, the liquid crystal element may be a passivematrix liquid crystal element or a segment liquid crystal element.

In the above embodiment, the display device preferably includes a firstsubstrate, a second substrate, and an insulating layer. It is preferablethat the insulating layer be between the first substrate and the secondsubstrate, the light-emitting element be between the first substrate andthe insulating layer, and the liquid crystal element be between thesecond substrate and the insulating layer. In addition, at least one ofthe first gate electrode, the first semiconductor layer, the firstsource electrode, and the first drain electrode is preferably in contactwith the insulating layer.

In the above embodiment, the display device preferably includes a wiringelectrically connected to the liquid crystal element. The firsttransistor and the wiring are preferably between the insulating layerand the first substrate, and the wiring is preferably electricallyconnected to the liquid crystal element in an opening in the insulatinglayer. The display device preferably further includes a secondtransistor electrically connected to the wiring. The wiring preferablyhas a function of transmitting visible light.

In the above embodiment, the display device preferably includes a firstwiring and a second wiring intersecting with each other. The firstwiring is preferably electrically connected to the first gate electrodeof the first transistor, and the second wiring is preferablyelectrically connected to one of the first source electrode and thefirst drain electrode of the first transistor. The first wiring and thesecond wiring can each have a function of blocking visible light.Alternatively, the first wiring and the second wiring may each have afunction of transmitting visible light.

According to one embodiment of the present invention, a display devicethat can switch display methods can be provided. Visibility insee-through display can be improved. A display device that can switchbetween normal display and see-through display can be provided. Adisplay device that offers high user safety can be provided.

A novel display device or a driving method of the novel display devicecan be provided. A highly reliable display device can be provided. Alightweight display device can be provided. A thin display device can beprovided.

Note that the description of these effects does not preclude theexistence of other effects. One embodiment of the present invention doesnot necessarily achieve all the effects listed above. Other effects canbe derived from the description of the specification, the drawings, theclaims, and the like.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 1C illustrate a structure example of a display device.

FIGS. 2A and 2B each illustrate a structure example of a display device.

FIGS. 3A1, 3A2, 3B1, and 3B2 illustrate structure examples of a displaydevice.

FIGS. 4A1, 4A2, 4B1, and 4B2 illustrate structure examples of a displaydevice.

FIGS. 5A and 5B illustrate a structure example of a display device.

FIGS. 6A to 6D illustrate a structure example of a display device.

FIGS. 7A to 7D illustrate a structure example of a display device.

FIGS. 8A and 8B illustrate a structure example of a display device.

FIGS. 9A and 9B illustrate a structure example of a display device.

FIG. 10 is a block diagram of an electronic device.

FIGS. 11A1, 11A2, 11B1, and 11B2 illustrate usage examples of electronicdevices.

FIG. 12 is a flow chart showing a driving method of an electronicdevice.

FIGS. 13A1, 13A2, 13B, 13C, and 13D illustrate a structure example of anelectronic device.

FIGS. 14A, 14B, 14C, 14D, 14E1, and 14E2 illustrate structure examplesof electronic devices.

FIG. 15 illustrates a structure example of a display panel.

FIGS. 16A to 16D illustrate a structure example of a display panel.

FIG. 17 illustrates a structure example of a display panel.

FIG. 18 illustrates a structure example of a display panel.

FIG. 19 illustrates a structure example of a display panel.

FIG. 20 illustrates a structure example of a display panel.

FIGS. 21A and 21B illustrate a structure of a transistor and electricalcharacteristics of the transistor according to Example 1.

FIG. 22 shows the sheet resistance of a conductive film according toExample 1.

FIG. 23 illustrates a structure of a light-emitting element according toExample 2.

FIG. 24 shows the voltage-transmittance characteristics of a liquidcrystal element according to Example 2.

FIGS. 25A to 25F illustrate a method for manufacturing a display deviceaccording to Example 2.

FIGS. 26A to 26C show the measurement results of transmittance accordingto Example 2.

FIG. 27 is a photograph of a display panel according to Example 2.

FIGS. 28A to 28D are photographs of a display panel according to Example2 and schematic views for showing states in photographing.

FIGS. 29A to 29D are schematic views of an optical system according toExample 3 and photographs of the optical system in a display state.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments will be described in detail with reference to the drawings.Note that the present invention is not limited to the followingdescription. It will be readily appreciated by those skilled in the artthat modes and details of the present invention can be modified invarious ways without departing from the spirit and scope of the presentinvention. Thus, the present invention should not be construed as beinglimited to the description in the following embodiments and example.

Note that in structures of the present invention described below, thesame portions or portions having similar functions are denoted by thesame reference numerals in different drawings, and a description thereofis not repeated. Further, the same hatching pattern is applied toportions having similar functions, and the portions are not especiallydenoted by reference numerals in some cases.

Note that in each drawing described in this specification, the size, thelayer thickness, or the region of each component is exaggerated forclarity in some cases. Therefore, the size, the layer thickness, or theregion is not limited to the illustrated scale.

Note that in this specification and the like, ordinal numbers such as“first,” “second,” and the like are used in order to avoid confusionamong components and do not limit the number.

A transistor is a kind of semiconductor elements and can achieveamplification of current or voltage, switching operation for controllingconduction or non-conduction, or the like. An insulated-gate fieldeffect transistor (IGFET) and a thin film transistor (TFT) are in thecategory of a transistor in this specification.

Note that the expressions indicating directions such as “over” and“under” are basically used to correspond to the directions of drawings.However, in some cases, the term “over” or “under” in the specificationindicates a direction that does not correspond to the apparent directionin the drawings, for the purpose of easy description or the like. As anexample, imagined is a situation where a stacked body is formed on acertain surface and a corresponding drawing apparently shows that thesurface on which the stacked body is provided (e.g., a formationsurface, a support surface, an attachment surface, or a planarizationsurface) is above the stacked body. In description of the stacked order(formation order) of the stacked body in the specification, a directionfrom the stacked body toward the surface may be expressed as “under” andthe opposite direction may be expressed as “over”.

Note that in this specification and the like, an EL layer means a layercontaining at least a light-emitting substance (also referred to as alight-emitting layer) or a stack including the light-emitting layer,provided between a pair of electrodes of a light-emitting element.

Note that in this specification and the like, a display panel as oneembodiment of the display device has a function of displaying(outputting) an image or the like on (to) a display surface; hence, thedisplay panel is one embodiment of an output device.

In this specification and the like, a structure in which a connectorsuch as a flexible printed circuit (FPC) or a tape carrier package (TCP)is attached to a substrate of a display panel, or a structure in whichan integrated circuit (IC) is mounted on a substrate by a chip on glass(COG) method or the like is referred to as a display panel module or adisplay module, or simply referred to as a display panel or the like insome cases.

Embodiment 1

In this embodiment, a display device of one embodiment of the presentinvention will be described.

One embodiment of the present invention is a display device in whichlight-emitting elements emitting visible light are arranged in matrix.An image can be displayed on the display surface side of the displaydevice by the light-emitting elements. The display device includes aliquid crystal element that overlaps with two adjacent light-emittingelements and a region between the two adjacent light-emitting elements.The liquid crystal element can make the transition between a state oftransmitting visible light (transmission state) and a state of blockingvisible light (non-transmission state).

When the liquid crystal element is in the transmission state, part ofexternal light entering from the side opposite to the display surfaceside is transmitted through the region between the two adjacentlight-emitting elements and extracted from the display surface side.Thus, an image displayed by the light-emitting elements can besuperimposed on a transmission image made by the transmitted externallight. This enables see-through display.

The light-emitting element preferably transmits visible light.Specifically, the light-emitting element preferably includes a pair ofelectrodes each of which has a light-transmitting property. Thisheightens the transmittance of the display device in see-throughdisplay.

When the liquid crystal element is in the non-transmission state, noexternal light is transmitted through the display device and thus onlyan image displayed by the light-emitting elements can be seen. Blockingexternal light transmission and using the light-emitting elements enabledisplay of an image that has an extremely high contrast and increasedsharpness. For example, the display device displaying an image for VRcan provide a stronger sense of immersion and reality.

In this manner, one embodiment of the present invention enablesswitching between two display modes. Specifically, one embodiment of thepresent invention enables switching between a transmission mode(see-through mode) by which the background behind the display device canbe seen through the display device and a light-emitting mode (emissionmode) by which high contrast display is performed with thelight-emitting elements.

For example, the display device of one embodiment of the presentinvention incorporated in a wearable (e.g., goggle-type or glasses-type)electronic device can be used as a display device that can freely switchbetween AR display and VR display. In AR display, a displayed image canbe superimposed on a transmission image without the use of an imagecaptured by a camera, which strengthens a sense of reality.

When used in a showcase or a window of a store, the above display devicecan heighten the advertising effect by utilizing switching between thetransmission mode and the light-emitting mode.

The display device of one embodiment of the present invention can beadopted not only for VR or AR application or for commercial use such asdigital signage but also for a variety of other applications.

As the light-emitting element included in the display device, an elementthat has a light source and performs display with light from the lightsource can be used. Specifically, it is preferable to use anelectroluminescence element where light can be extracted from alight-emitting substance by application of an electric field. Since theluminance and the chromaticity of light emitted from such a pixel arenot affected by external light, an image with high color reproducibility(a wide color gamut) and a high contrast, i.e., a clear image can bedisplayed.

As the light-emitting element, for example, a self-luminouslight-emitting element such as an organic light-emitting diode (OLED), alight-emitting diode (LED), a quantum-dot light-emitting diode (QLED),or a semiconductor laser can be suitably used.

The liquid crystal element included in the display device is preferablya normally black liquid crystal element that blocks light when appliedwith no electric field. This heightens a contrast in the light-emittingmode; in addition, this reduces power consumption because application ofan electric field is unnecessary in the light-emitting mode.

It is preferable that the light-emitting element be provided on thedisplay surface side and the liquid crystal element be provided on theside (back surface side) opposite to the display surface side with theinsulating layer between the light-emitting element and the liquidcrystal element. This structure can decrease the number of layerspresent on the path of light from the light-emitting element, improvinglight extraction efficiency and heightening color reproducibility.

Instead of the liquid crystal element, any of various elements that canswitch between the state of transmitting visible light and the state ofnot transmitting visible light may be used.

It is preferable to adopt an active matrix method by which the pluralityof light-emitting elements are each connected to one or moretransistors. It is preferable that both a transistor electricallyconnected to the light-emitting element and a wiring connected to theliquid crystal element be provided on the same surface side of theinsulating layer. It is preferable that either electrical connectionbetween the light-emitting element and the transistor or that betweenthe liquid crystal element and the wiring be made in an opening providedin the insulating layer.

A display region preferably includes a plurality of pixels provided withthe light-emitting elements. The pixel may include a plurality ofsubpixels. Part or all of wirings and electrodes in the pixel preferablyinclude light-transmitting conductive films (e.g., an oxide conductivefilm). In that case, a portion where light-transmitting wirings orelectrodes are provided can be used as a region that transmits visiblelight (transmission region), which improves transmittance in see-throughdisplay.

In particular, when a semiconductor layer, a source electrode, a drainelectrode, a gate electrode, and the like of a transistor in the displayregion have a light-transmitting property, a region where a transistoris provided can also be used as the transmission region.

A contact portion connecting two wirings between which an insulatinglayer or the like is provided can also be used as the transmissionregion when these wirings include conductive films that transmit visiblelight.

The use of a conductive film having no light-transmitting property(e.g., a metal film) for other part of wirings in the display region canreduce wiring resistance. A bus line such as a scan line, a signal line,or a power supply line preferably includes a non-light-transmittingmaterial with low electric resistance such as a metal. Note that wiringsin a small display region (e.g., a display region with a size smallerthan one inch diagonal) can be small in length, and thus all the wiringsmay include light-transmitting conductive films to heighten the lighttransmittance.

In contrast, a wiring, a driver circuit, or the like outside the displayregion preferably includes a conductive film that transmits no visiblelight. This reduces a resistance component of the wiring, the drivercircuit, or the like, leading to high-speed operation.

One liquid crystal element may be provided in the transmission region ofeach pixel. Alternatively, the display region may be divided intoseveral areas and one liquid crystal element may be provided per areaincluding some light-emitting elements. Alternatively, one liquidcrystal element may be provided across the entire display region. Aplurality of liquid crystal elements enables display including both aregion displayed in the transmission mode and a region displayed in thelight-emitting mode. For example, see-through display can be performedpartly.

When a plurality of liquid crystal elements are used, segment liquidcrystal elements, passive matrix liquid crystal elements, or activematrix liquid crystal elements can be employed. A segment liquid crystalelement or a passive matrix liquid crystal element is connected to awiring in the display region. An active matrix liquid crystal element isconnected to one or more transistors in the display region.

A wiring, a transistor, or the like that is electrically connected to aliquid crystal element also preferably includes a conductive film thattransmits visible light.

The light-emitting elements are preferably arranged in the displayregion in such a way as to give extremely high definition. Higherdefinition is more preferable; specifically, the light-emitting elementsare preferably arranged in the display region to give a definitionhigher than or equal to 300 ppi and lower than or equal to 10,000 ppi,preferably higher than or equal to 500 ppi and lower than or equal to5,000 ppi, further preferably higher than or equal to 700 ppi and lowerthan or equal to 4,000 ppi, or still further preferably higher than orequal to 1,000 ppi and lower than or equal to 3,000 ppi. Such ahigh-definition display device can be suitably used in a device with arelatively short viewing distance, such as a wearable (e.g., goggle-typeor glasses-type) electronic device or a mobile information terminal.

Digital signage or a large display device, which presumably has arelatively long viewing distance (e.g., 1 m or longer), does not requirea high definition; thus, a definition higher than or equal to 1 ppi andlower than 300 ppi may be acceptable.

A more specific example is described below with reference to drawings.

[Structure Example]

FIG. 1A illustrates an example of a cross-sectional structure of adisplay device 10.

The display device 10 includes a functional layer 45, an insulatinglayer 81, an insulating layer 83, a light-emitting element 90, a liquidcrystal element 40, and the like between a substrate 21 and a substrate31. A polarizing plate 39 a is provided on the outer side of thesubstrate 21, and a polarizing plate 39 b is provided on the outer sideof the substrate 31. The substrate 21 side corresponds to the displaysurface side of the display device 10.

The light-emitting element 90 includes a conductive layer 91, aconductive layer 93, and an EL layer 92 between the conductive layers 91and 93. The EL layer 92 includes at least a light-emitting substance.The conductive layer 91 is provided for each pixel (each subpixel) andfunctions as a corresponding pixel electrode. The conductive layer 93 isshared by a plurality of pixels. The conductive layer 93 is connected toa wiring supplied with a constant potential in a region that is notillustrated and functions as a common electrode.

The conductive layers 91 and 93 in the light-emitting element 90transmit visible light. Thus, the light-emitting element 90 is adual-emission light-emitting element that emits light to both thesubstrate 21 side and the substrate 31 side by application of a voltagebetween the conductive layers 91 and 93. The light-emitting element 90transmits visible light, and thus can serve as part of the transmissionregion.

The liquid crystal element 40 includes a conductive layer 23, aconductive layer 25, and a liquid crystal 24 between the conductivelayers 23 and 25. The conductive layers 23 and 25 each transmit visiblelight. Thus, the liquid crystal element 40 is a transmissive liquidcrystal element that can control the amount of visible light to betransmitted.

The conductive layers 23 and 25 are connected to different wirings in aregion not illustrated. One of the two wirings is supplied with a fixedpotential, and the other is supplied with a signal (potential) forcontrolling the orientation state of the liquid crystal element.

Here, the conductive layers 23 and 25 overlap with a plurality oflight-emitting elements 90. That is, the liquid crystal element 40 isprovided across a plurality of pixels.

The functional layer 45 includes a circuit for driving thelight-emitting element 90. For example, the functional layer 45 includesa pixel circuit including a transistor, a capacitor, a wiring, anelectrode, and the like.

At least one of a gate electrode, a semiconductor layer, a sourceelectrode, and a drain electrode of the transistor in the functionallayer 45 has a light-transmitting property. It is particularlypreferable that all of them have a light-transmitting property. In thatcase, the transistor transmits visible light, and thus can serve as partof the transmission region.

The capacitor, the wiring, the electrode, and the like in the functionallayer 45 preferably have a light-transmitting property. This increasesthe area of the transmission region, improving visibility in see-throughdisplay.

Wirings connected to a plurality of functional layers 45 may include anon-light-transmitting conductive material with low electric resistancesuch as a metal. This reduces wiring resistance. Alternatively, thewiring may include a light-transmitting conductive material. This allowsa portion where the wiring is provided to be the transmission region.

The insulating layer 83 is provided between the functional layer 45 andthe conductive layer 23. The conductive layer 23 may be electricallyconnected to a wiring provided on the substrate 31 side of theinsulating layer 83 in a region not illustrated. Alternatively, theconductive layer 23 may be electrically connected to a wiring that iscloser to the substrate 21 than the insulating layer 83 is, in anopening provided in the insulating layer 83 in a region not illustrated.

The insulating layer 81 is provided between the functional layer 45 andthe conductive layer 91. The conductive layer 91 and the functionallayer 45 are electrically connected to each other in an opening providedin the insulating layer 81. In this way, the functional layer 45 and thelight-emitting element 90 are electrically connected to each other.

The insulating layer 84 is provided to cover an end portion of theconductive layer 91, and the EL layer 92 is provided to cover part ofthe insulating layer 84 and part of the conductive layer 91.Furthermore, the conductive layer 93 is provided to cover the EL layer92.

An adhesive layer 89 is provided between the substrate 21 and theconductive layer 93. It can also be said that the substrate 21 and thesubstrate 31 are attached to each other with the adhesive layer 89. Theadhesive layer 89 also functions as a sealing layer that seals thelight-emitting element 90.

In this way, the two kinds of display elements (the liquid crystalelement 40 and the light-emitting element 90) and the functional layer45 for driving the light-emitting element are provided between the pairof substrates, which leads to a reduction in thickness.

The liquid crystal element 40 and the light-emitting element 90 overlapwith each other with the insulating layer 83, the functional layer 45,and the like therebetween. This structure enables, for example, areduction in a distance between the liquid crystal element 40 and thelight-emitting element 90 and a decrease in the number of layerssandwiched between these elements as compared with a structure in whicha display panel including a light-emitting element and a display panelincluding a liquid crystal element are attached to each other. Thus,this structure can provide a clearer transmission image.

For example, a distance between the upper surface of the conductivelayer 23 in the liquid crystal element 40 and the lower surface of theconductive layer 91 in the light-emitting element 90 can be longer thanor equal to 20 nm and shorter than 30 μm, preferably longer than orequal to 50 nm and shorter than 10 μm, or more preferably longer than orequal to 100 nm and shorter than 5 μm.

A coloring layer CFR, a coloring layer CFG, and a coloring layer CFB areeach provided on the substrate 31 side of the substrate 21 to overlapwith the corresponding light-emitting element 90. The coloring layerCFR, the coloring layer CFG, and the coloring layer CFB serve as colorfilters transmitting red light, green light, and blue light,respectively. Thus, color display can be performed with thelight-emitting elements 90 that emit white light.

In FIG. 1A, the EL layer 92 is uniformly provided to be included in theplurality of light-emitting elements 90. Here, each of thelight-emitting elements 90 is a light-emitting element that emits whitelight. Accordingly, light emitted from the light-emitting element 90provided with the coloring layer CFR passes through the coloring layerCFR and is emitted to the display surface side as red light 20R.Similarly, green light 20G is emitted from the light-emitting element 90provided with the coloring layer CFG, and blue light 20B is emitted fromthe light-emitting element 90 provided with the coloring layer CFB.

A region between two adjacent light-emitting elements 90 includes aregion provided with no light-blocking member and serving as thetransmission region. When the liquid crystal element 40 is in thetransmission state, transmission light 20 t transmitted through theliquid crystal element 40 passes through that region from the substrate31 side to the substrate 21 side. From the display surface side, a usercan see a transmission image of the background behind the display device10.

The region between the two adjacent light-emitting elements 90 ispreferably provided with no coloring layer. This prevents absorption ofpart of the transmission light 20 t by a coloring layer, providing aclearer transmission image.

Since the light-emitting element 90 has a light-transmitting property, aportion including the light-emitting element 90 serves as thetransmission region. Three rays of the transmission light 20 ttransmitted through the coloring layers CFR, CFG, and CFB are mixed incolor and the mixed color is recognized by a user; accordingly, changein color tone can be suppressed.

The liquid crystal element 40 is preferably a normally black liquidcrystal element that blocks visible light when applied with no electricfield. Arrangement of the polarizing plates 39 a and 39 b are preferablyadjusted so that the liquid crystal element 40 serves as a normallyblack liquid crystal element. As the polarizing plate, a linearpolarizing plate can be used. Alternatively, a circularly polarizingplate in which a linear polarizing plate and a quarter-wave retardationplate are stacked may be used. When the polarizing plate 39 a on thedisplay surface side is a circularly polarizing plate, reflection ofexternal light can be reduced. Note that the positions of the polarizingplates 39 a and 39 b are not limited to those illustrated in FIG. 1A, aslong as the liquid crystal element 40 is between the polarizing plates39 a and 39 b. For example, the polarizing plate 39 a may be positionedbetween the conductive layer 23 and the substrate 21.

Depending on the structure of the liquid crystal element 40, one or bothof the polarizing plates 39 a and 39 b may be omitted. For example, theuse of a guest-host liquid crystal element as the liquid crystal element40 can eliminate the polarizing plate 39 a. This can further increasethe light extraction efficiency of the light-emitting element 90. Theuse of a dispersed liquid crystal element as the liquid crystal element40 can eliminate both polarizing plates. A decrease in the number ofpolarizing plates can increase the brightness of the transmission lightin the transmission mode. In addition, the use of a guest-host liquidcrystal element can prevent emitted light from the rear surface side ofthe light-emitting element 90 from leaking to the outside.

Note that any of a variety of optical members can be arranged on theouter side of the substrate 21. Examples of the optical members includea light diffusion layer (e.g., a diffusion film), an anti-reflectivelayer, and a light-condensing film in addition to the polarizing plateand the retardation plate. Furthermore, an antistatic film preventingthe attachment of dust, a water repellent film suppressing theattachment of stain, a hard coat film suppressing generation of ascratch caused by the use, or the like may be arranged on the outer sideof the substrate 21.

A touch sensor may be provided on the outer side of the substrate 21.Thus, a structure including the display device 10 and the touch sensorcan function as a touch panel.

The display device 10 can switch between the light-emitting mode(emission mode) in which an image is displayed by the light-emittingelements with the liquid crystal element 40 in the non-transmissionstate and the transmission mode (see-through mode) in which an imagedisplayed by the light-emitting elements is superimposed on atransmission image with the liquid crystal element 40 in thetransmission state.

FIG. 1B is a schematic diagram of the display device in thelight-emitting mode.

The light-emitting elements 90 can emit light 20 e to the displaysurface side to display an image.

The liquid crystal element 40 has an orientation for blocking visiblelight. When the liquid crystal element 40 is a normally black liquidcrystal element, an electric field is not applied to the liquid crystalelement 40. Light 20in entering from the back surface of the displaydevice 10 cannot go through the display device 10, and thus does notreach user's eyes. Specifically, the light 20in entering from the backsurface of the display device 10 is polarized by the polarizing plate 39b, transmitted through the liquid crystal element 40, and blocked by thepolarizing plate 39 a.

As described above, the light-emitting mode does not allow the light20in entering from the back surface of the display device 10 to reach auser, and thus enables high contrast display. Such a mode can also bereferred to as a VR mode.

FIG. 1C is a schematic diagram of the display device in the transmissionmode.

The light-emitting elements 90 can emit the light 20 e to the displaysurface side to display an image, as in the light-emitting mode.

The liquid crystal element 40 has an orientation for transmittingvisible light. When the liquid crystal element 40 is a normally blackliquid crystal element, a sufficient electric field is applied to theliquid crystal element 40. The light 20in entering from the back surfaceof the display device 10 goes through the display device 10, and reachesuser's eyes. Specifically, the light 20in entering from the back surfaceof the display device 10 is transmitted through the polarizing plate 39b, the liquid crystal element 40, and the polarizing plate 39 a andcasted to the display surface side as the transmission light 20 t.

Therefore, the transmission mode allows a user to see both the light 20e from the light-emitting elements 90 and the transmission light 20 t.That is, the image displayed with the light-emitting elements 90 can besuperimposed on the background (transmission image) behind the displaydevice 10. Such a mode can also be referred to as an AR mode.

Controlling the magnitude of the electric field applied to the liquidcrystal element 40 enables controlling the amount of the transmissionlight 20 t. For example, in the case where incident light from the sun,a light source, or the like is too bright to make a user dazzled, thedegree of dazzle can be reduced by controlling the orientation in theliquid crystal element 40 and decreasing the amount of the transmissionlight 20 t.

A gradual increase in voltage applied to the liquid crystal element 40enables continuous change from the state of blocking external light tothe state of transmitting external light at maximum, for example. Theinverse continuous change from the state of transmitting external lightat maximum to the state of blocking external light is also possible.This can prevent rapid change in luminance of the transmission light 20t entering user's eyes, and avoid making a user uncomfortable.

The above is the description of the structure example.

MODIFICATION EXAMPLE

A structure example partly different from that shown in FIG. 1A isdescribed below.

Modification Example 1

As contrasted with the above example where color display is achieved bythe light-emitting element 90 that can emit white light in combinationwith the coloring layer CFR, CFG, or CFB, the following example employslight-emitting elements each of which can emit colored light of red,green, blue, or the like.

FIG. 2A shows an example where a light-emitting element 90R that emitsthe red light 20R, a light-emitting element 90G that emits the greenlight 20G, and a light-emitting element 90B that emits the blue light20B are provided instead of the light-emitting element 90 illustrated inFIG. 1A. The coloring layers CFR, CFG, and CFB illustrated in FIG. 1Aare not provided.

The light-emitting element 90R, the light-emitting element 90G, and thelight-emitting element 90B include an EL layer 92R, an EL layer 92G, andan EL layer 92B, respectively. The conductive layer 93 covers the ELlayer 92R, the EL layer 92G, and the EL layer 92B.

With such a structure, the light extraction efficiencies of thelight-emitting elements 90R, 90G, and 90B can be increased, so thatpower consumption can be reduced.

Part of layers constituting the EL layers may be formed separately forthe light-emitting elements 90R, 90G, and 90B while the other layers areshared by the light-emitting elements 90R, 90G, and 90B. For example,only the light-emitting layers may be separately formed.

Alternatively, among the light-emitting layers of three colors, alight-emitting layer exhibiting a color with the shortest wavelength(e.g., a light-emitting layer that emits blue light) may be shared byanother display element. This simplifies a formation process of thelight-emitting elements 90R, 90G, and 90B.

Modification Example 2

Although the liquid crystal element 40 is provided across the pluralityof pixels in the above structure, the liquid crystal element 40 can beprovided per pixel.

FIG. 2B shows an example where a plurality of liquid crystal elements 40each provided with the island-shaped conductive layer 23 are provided.Such a structure enables switching between the transmission mode and thelight-emitting mode in each transmission region.

The structure in FIG. 2B includes a functional layer 45 a and afunctional layer 45 b. The functional layer 45 a includes a circuit fordriving the light-emitting element. The functional layer 45 b serves asa pixel circuit for controlling the driving of the liquid crystalelement 40, and includes at least one transistor. The conductive layer23 and the functional layer 45 b are electrically connected to eachother in an opening provided in the insulating layer 83. Such astructure allows the liquid crystal element 40 to be an active matrixliquid crystal element. When the functional layer 45 b just includes awiring without a transistor, the liquid crystal element 40 can be asegment liquid crystal element or a passive matrix liquid crystalelement.

At least one of a gate electrode, a semiconductor layer, a sourceelectrode, and a drain electrode of the transistor in the functionallayer 45 b preferably has a light-transmitting property. It isparticularly preferable that all of them have a light-transmittingproperty. In that case, the transistor transmits visible light, and thuscan serve as part of the transmission region.

A capacitor, a wiring, an electrode, and the like in the functionallayer 45 b preferably have a light-transmitting property. This increasesthe area of the transmission region, improving visibility in see-throughdisplay.

Wirings connected to a plurality of functional layers 45 b may include anon-light-transmitting conductive material with low electric resistancesuch as a metal. This reduces wiring resistance. Alternatively, thewiring may include a light-transmitting conductive material. This allowsa portion where the wiring is provided to be the transmission region.

Here, one liquid crystal element 40 is provided per light-emittingelement 90; however, one liquid crystal element 40 may be provided everysome light-emitting elements 90.

Example 1 of Pixel Layout

An example of a pixel layout is described below.

FIG. 3A1 is a schematic top view of a pixel 30 seen from the displaysurface side. The pixel 30 includes three subpixels including thelight-emitting elements 90R, 90G, and 90B. Each subpixel includes atransistor 61 and a transistor 62. The pixel 30 further includes theliquid crystal element 40, a wiring 51, a wiring 52, a wiring 53, andthe like.

The wiring 51 serves as a scan line, for example. The wiring 52 servesas a signal line, for example. The wiring 53 serves as a line forsupplying a potential to the light-emitting element, for example. Thewiring 51 intersects with the wiring 52. In this example, the wiring 53is parallel to the wiring 52. The wiring 53 may be parallel to thewiring 51.

The transistor 61 serves as a selection transistor. A gate of thetransistor 61 is electrically connected to the wiring 51, and one of asource and a drain of the transistor 61 is electrically connected to thewiring 52. The transistor 62 controls a current flowing in thelight-emitting element. One of a source and a drain of the transistor 62is electrically connected to the wiring 53, and the other iselectrically connected to the light-emitting element.

In FIG. 3A1, the light-emitting elements 90R, 90G, and 90B each have astrip shape long in the vertical direction, and they are arranged in thehorizontal direction to form a striped pattern.

As described in the above structure example and the like, the liquidcrystal element 40 is positioned closer to the back surface (opposite tothe display surface) than the light-emitting elements or wirings are.FIG. 3A1 shows a region that overlaps with no light-emitting element orwiring and allows the liquid crystal element 40 to be seen from thedisplay surface side. That region is part of the transmission region. Inthe transmission mode, light entering from the back surface of thedisplay device is transmitted through that transmission region.

The wirings 51, 52, and 53 have a light-blocking property. Other layers,i.e., layers constituting the transistor 61, the transistor 62, or thelike are light-transmitting films. FIG. 3A2 shows separately atransmission region 30 t that transmits visible light and alight-blocking region 30 s that blocks visible light that are in thepixel 30 of FIG. 3A1. The entire portion except a portion includingwirings is the transmission region 30 t, whereby visibility insee-through display can be improved.

FIGS. 3B1 and 3B2 illustrate an example where the pixel 30 includes foursubpixels including the light-emitting elements 90R, 90G, and 90B and alight-emitting element 90W. In the example of FIGS. 3B1 and 3B2, thelight-emitting elements are arranged in two columns and two rows in onepixel 30. In FIG. 3B1, the pixel 30 includes the two wirings 51, the twowirings 52, and the two wirings 53.

The light-emitting element 90W can be a light-emitting element thatemits white light, for example. When the cross-sectional structure shownin FIG. 1A is employed, the light-emitting element 90W may overlap withno coloring layer.

A region that overlaps with no wiring is the transmission region 30 t,as shown in FIG. 3B2.

The higher the proportion of the area of the transmission region in thearea of the display region is, the larger the amount of the transmissionlight is. The proportion of the area of the transmission region in thearea of the entire display region is, for example, greater than or equalto 1% and less than or equal to 95%, preferably greater than or equal to10% and less than or equal to 90%, or more preferably greater than orequal to 20% and less than or equal to 80%. A particularly preferableproportion is greater than or equal to 40% or greater than or equal to50%. The large transmission region enables switching between thelight-emitting mode and the transmission mode without giving a user afeeling of strangeness.

FIGS. 4A1 and 4A2 show an example where the wirings 51, 52, and 53 ofFIGS. 3A1 and 3A2 have a light-transmitting property. Similarly, FIGS.4B1 and 4B2 show an example where the wirings 51, 52, and 53 of FIGS.3B1 and 3B2 have a light-transmitting property. The structures shown inFIGS. 4A2 and 4B2 each allow the entire region of the pixel 30 to be thetransmission region 30 t.

Example 2 of Pixel Layout

An example of a pixel layout suitable for a high-definition displaydevice is described below.

For example, a display device with a structure shown below can havepixels with light-emitting elements that are arranged to give adefinition higher than or equal to 300 ppi and lower than or equal to10,000 ppi, preferably higher than or equal to 500 ppi and lower than orequal to 5,000 ppi, further preferably higher than or equal to 700 ppiand lower than or equal to 4,000 ppi, or still further preferably higherthan or equal to 1,000 ppi and lower than or equal to 3,000 ppi.

[Structure Example of Pixel Circuit]

FIG. 5A is an example of a circuit diagram of a pixel unit 70. The pixelunit 70 includes two pixels (a pixel 70 a and a pixel 70 b). Inaddition, the pixel unit 70 is connected to wirings 51 a, 51 b, 52 a, 52b, 52 c, 52 d, 53 a, 53 b, and 53 c and the like.

The pixel 70 a includes subpixels 71 a, 72 a, and 73 a. The pixel 70 bincludes subpixels 71 b, 72 b, and 73 b. The subpixels 71 a, 72 a, and73 a include pixel circuits 41 a, 42 a, and 43 a, respectively. Thesubpixels 71 b, 72 b, and 73 b include pixel circuits 41 b, 42 b, and 43b, respectively.

Each subpixel includes a pixel circuit and a display element 60. Forexample, the subpixel 71 a includes a pixel circuit 41 a and the displayelement 60. A light-emitting element such as an organic EL element isused here as the display element 60.

The wirings 51 a and 51 b each serve as a scan line (also referred to asa gate line). The wirings 52 a, 52 b, 52 c, and 52 d each serve as asignal line (also referred to as a source line or a data line). Thewirings 53 a, 53 b, and 53 c each have a function of supplying apotential to the display element 60.

The pixel circuit 41 a is electrically connected to the wirings 51 a, 52a, and 53 a. The pixel circuit 42 a is electrically connected to thewirings 51 b, 52 d, and 53 a. The pixel circuit 43 a is electricallyconnected to the wirings 51 a, 52 b, and 53 b. The pixel circuit 41 b iselectrically connected to the wirings 51 b, 52 a, and 53 b. The pixelcircuit 42 b is electrically connected to the wirings 51 a, 52 c, and 53c. The pixel circuit 43 b is electrically connected to the wirings 51 b,52 b, and 53 c.

With the structure shown in FIG. 5A in which two gate lines areconnected to each pixel, the number of source lines can be reduced byhalf of the stripe arrangement. As a result, the number of ICs used assource driver circuits can be reduced by half and accordingly the numberof components can be reduced.

A wiring functioning as a signal line is preferably connected to pixelcircuits of the same color. For example, when a signal with an adjustedpotential supplied to the wiring corrects for variation in luminancebetween pixels, the correction value may greatly vary between colors.Thus, when pixel circuits connected to one signal line correspond to thesame color, the correction can be performed easily.

In addition, each pixel circuit includes a transistor 61, a transistor62, and a capacitor 63. In the pixel circuit 41 a, for example, a gateof the transistor 61 is electrically connected to the wiring 51 a, oneof a source and a drain of the transistor 61 is electrically connectedto the wiring 52 a, and the other of the source and the drain iselectrically connected to a gate of the transistor 62 and one electrodeof the capacitor 63. One of a source and a drain of the transistor 62 iselectrically connected to one electrode of the display element 60, andthe other of the source and the drain is electrically connected to theother electrode of the capacitor 63 and the wiring 53 a. The otherelectrode of the display element 60 is electrically connected to awiring to which a potential V1 is applied.

Note that the other pixel circuits are similar to the pixel circuit 41 aexcept a wiring connected to the gate of the transistor 61, a wiringconnected to the one of the source and the drain of the transistor 61,or a wiring connected to the other electrode of the capacitor 63 (seeFIG. 5A).

In FIG. 5A, the transistor 61 serves as a selection transistor. Thetransistor 62 is in a series connection with the display element 60 tocontrol a current flowing in the display element 60. The capacitor 63has a function of holding the potential of a node connected to the gateof the transistor 62. Note that the capacitor 63 does not have to beintentionally provided in the case where an off-state leakage current ofthe transistor 61, a leakage current through the gate of the transistor62, and the like are extremely small.

The transistor 62 preferably includes a first gate and a second gateelectrically connected to each other as shown in FIG. 5A. The amount ofcurrent that the transistor 62 can supply can be increased owing to thetwo gates. Such a structure is particularly preferable for ahigh-resolution display device because the amount of current can beincreased without increasing the size, the channel width in particular,of the transistor 62.

Note that the number of gates of the transistor 62 may be one. Thisstructure can be manufactured in a simpler process than the abovestructure because a step of forming the second gate is unnecessary. Thetransistor 61 may have two gates. This structure enables a reduction insize of the transistors. A first gate and a second gate of eachtransistor can be electrically connected to each other. Alternatively,the gates may be electrically connected to different wirings. In thiscase, threshold voltages of the transistors can be controlled byapplying different potentials to the wirings.

The electrode of the display element 60 that is electrically connectedto the transistor 62 corresponds to a pixel electrode (e.g., theconductive layer 91). In FIG. 5A, the one of the electrodes of thedisplay element 60 that is electrically connected to the transistor 62serves as a cathode, whereas the other electrode serves as an anode.This structure is particularly effective when the transistor 62 is ann-channel transistor. When the n-channel transistor 62 is on, thepotential applied from the wiring 53 a is a source potential;accordingly, the amount of current flowing in the transistor 62 can beconstant regardless of variation or change in resistance of the displayelement 60. Alternatively, a p-channel transistor may be used as atransistor of a pixel circuit.

[Example of Pixel Electrode Arrangement]

FIG. 5B is a schematic top view showing an arrangement example of pixelelectrodes and wirings in the display region. The wirings 51 a and 52 bare alternately arranged. The wirings 52 a, 52 b, and 52 c are arrangedin this order to intersect with the wirings 51 a and 51 b. The pixelelectrodes are arranged in matrix in the extending direction of thewirings 51 a and 51 b.

The pixel unit 70 includes the pixels 70 a and 70 b. The pixel 70 aincludes a pixel electrode 91R1, a pixel electrode 91G1, and a pixelelectrode 91B1. The pixel 70 b includes a pixel electrode 91R2, a pixelelectrode 91G2, and a pixel electrode 91B2. A display region of eachsubpixel is inside the pixel electrode of the subpixel.

As shown in FIG. 5B, a pitch of the pixel units 70 arranged in theextending direction of the wiring 52 a or the like (also referred to asthe first direction) is denoted as P. A pitch of the pixel units 70arranged in the extending direction of the wiring 51 a or the like (alsoreferred to as the second direction) is preferably twice the pitch P(i.e., preferably the pitch 2P). In that case, distortion-free imagescan be displayed. The pitch P can be longer than or equal to 1 μm andshorter than or equal to 150 μm, preferably longer than or equal to 2 μmand shorter than or equal to 120 μm, further preferably longer than orequal to 3 μm and shorter than or equal to 100 μm, and still furtherpreferably longer than or equal to 4 μm and shorter than or equal to 60μm. Such a structure allows the display device to have extremely highdefinition.

It is preferable that the pixel electrode 91R1 should not overlap withthe wiring 52 a serving as a signal line and the like, for example. Thiscan suppress change in luminance of the display element, which is causedby change in potential of the pixel electrode 91R1 and the like due totransmission of electrical noise through capacitance between, forexample, the wiring 52 a and the pixel electrode 91R1.

The pixel electrode 91R1 and the like may overlap with the wiring 51 aor the like serving as a scan line. This can increase the area of thepixel electrode 91R1 and the aperture ratio. In the example of FIG. 5B,part of the pixel electrode 91R1 overlaps with the wiring 51 a.

When the pixel electrode 91R1 or the like of a subpixel overlaps withthe wiring 51 a or the like serving as a scan line, the wiring servingas a scan line and overlapping with the pixel electrode is preferablyconnected to a pixel circuit of the subpixel. For example, a period inwhich a signal for changing the potential of the wiring 51 a or the likeis input corresponds to a period in which data of the subpixel isrewritten. Thus, if electrical noise would transmit from the wiring 51 aor the like to the overlapping pixel electrode via capacitance, theluminance of the subpixel does not change.

Example 1 of Pixel Layout

A layout example of the pixel unit 70 is described below.

FIG. 6A is a layout example of a subpixel. The example shows, for easyviewing, a state before a pixel electrode is formed. The subpixel shownin FIG. 6A includes the transistor 61, the transistor 62, and thecapacitor 63. The transistor 61 is a bottom-gate channel-etchedtransistor. The transistor 62 includes two gates with a semiconductorlayer therebetween.

A conductive layer 56 at a lower position forms lower gate electrodes ofthe transistors 61 and 62, one electrode of the capacitor 63, and thelike. A conductive layer that is formed after the formation of theconductive layer 56 forms the wiring 51. A conductive layer 57 that isformed thereafter forms one of a source electrode and a drain electrodeof the transistor 61, a source electrode and a drain electrode of thetransistor 62, and the like. A conductive layer that is formed after theformation of the conductive layer 57 forms the wiring 52, the wiring 53,and the like. A conductive layer 58 that is formed thereafter forms anupper gate electrode of the transistor 62. Part of the wiring 52 servesas the other of the source electrode and the drain electrode of thetransistor 61. Part of the wiring 53 serves as the other electrode ofthe capacitor 63. For easy viewing, the conductive layer 58 is shownjust with its outline without a hatching pattern.

The semiconductor layer 55, the conductive layer 56, the conductivelayer 57, and the conductive layer 58 that are included in thetransistors each have a light-transmitting property. The wirings 51, 52,and 53 each have a light-blocking property.

In FIG. 6B, the transmission region 30 t and the light-blocking region30 s in the subpixel shown in FIG. 6A are separately shown. As shown inthe drawing, the transistors 61 and 62 and the like have alight-transmitting property; accordingly, visibility in see-throughdisplay can be heightened.

For example, such a structure allows the proportion of the area of thetransmission region 30 t (also referred to as an aperture ratio) to behigher than or equal to 50%. The structure shown in FIGS. 6A and 6Bachieves an aperture ratio of approximately 66.1% or higher.

FIG. 6C is a layout example of the pixel unit 70 including the subpixelshown in FIG. 6A. FIG. 6C also shows pixel electrodes and displayregions 22. This example shows a dual-emission light-emitting element asthe light-emitting element. FIG. 6C is a schematic top view seen fromthe display surface side. In FIG. 6D, the transmission region 30 t andthe light-blocking region 30 s in FIG. 6C are separately shown.

In this example, three subpixels electrically connected to the wiring 51a have shapes laterally inverted from the shapes of the three subpixelselectrically connected to the wiring 51 b. Therefore, in the structurein which same-color subpixels are arranged in a zigzag pattern in theextending direction of the wiring 52 a or the like and are connected toone wiring serving as a signal line, wirings connected to the subpixelscan have uniform length, so that variation in luminance between thesubpixels can be suppressed.

With use of such a pixel layout, a display device with extremely highdefinition can be fabricated even in a production line in which theminimum feature size is greater than or equal to 0.5 μm and smaller thanor equal to 6 μm, typically greater than or equal to 1.5 μm and smallerthan or equal to 4 μm.

FIG. 6C shows the liquid crystal element 40 that is positioned closer tothe back surface (opposite to the display surface) than thelight-emitting elements and wirings are.

Example 2 of Pixel Layout

FIGS. 7A and 7B show a layout example different from that shown in FIGS.6A and 6B.

The transistor 61 is a top-gate transistor. The transistor 62 includesthe two gates with the semiconductor layer therebetween.

In FIG. 7A, the conductive layer 57 at a lower position forms one gateelectrode of the transistor 62, and the semiconductor layer 55 is formedafter the formation of the conductive layer 57. The conductive layer 56that is formed after the formation of the conductive layer 57 and thesemiconductor layer 55 forms a gate electrode of the transistor 61 andthe other gate electrode of the transistor 62. A conductive layer thatis formed after the formation of the conductive layer 56 forms thewiring 51 and the like. A conductive layer that is formed thereafterforms the wiring 52, one electrode of the capacitor 63, and the like. Aconductive layer that is formed thereafter forms the wiring 53 and thelike.

The semiconductor layer 55, the conductive layer 56, and the conductivelayer 57 have a light-transmitting property. The structure shown inFIGS. 7A and 7B achieves an aperture ratio of approximately 37.1% orhigher.

The transistor 61 includes the semiconductor layer 55 over the wiring51, part of the wiring 52, and the like. The transistor 62 includes theconductive layer 57, the semiconductor layer 55 over the conductivelayer 57, the wiring 53, and the like. The capacitor 63 includes part ofthe wiring 53 and a conductive layer that is on the same plane as thewiring 52.

FIGS. 7C and 7D illustrate a structure example of a pixel unit includingthe subpixel shown in FIG. 7A.

FIG. 7C shows the liquid crystal element 40 that is positioned closer tothe back surface (opposite to the display surface) than thelight-emitting elements and wirings are.

Example 3 of Pixel Layout

FIGS. 8A and 8B show a layout example of a subpixel 50 different fromthe layout examples shown in FIGS. 6A and 6B and FIGS. 7A and 7B.

The subpixel 50 includes transistors 61 a, 61 b, and 62. The transistors61 a, 61 b, and 62 each include two gates with a semiconductor layertherebetween. FIG. 8A also shows a pixel electrode 64 and the displayregion 22. The pixel electrode 64 is shared by an adjacent pixel (notillustrated).

The transistor 62 in FIG. 8A has a stacked-layer structure similar tothat of the transistor 62 in FIG. 7A.

The transistor 61 a includes the semiconductor layer 55 over the wiring51, the conductive layer 58 over the semiconductor layer 55, aconductive layer connected to a wiring 59 supplied with a constantpotential, and the like. The transistor 61 b includes the semiconductorlayer 55 over the wiring 51, the conductive layer 58 over thesemiconductor layer 55, a conductive layer connected to the wiring 52,and the like. The conductive layer 58 is connected to the wiring 59. Thewiring 51 and the conductive layer 58 serve as gate electrodes.

The wirings 51, 52, 53, and 59 have a light-blocking property. Otherlayers, i.e., layers constituting the transistor 61 a, 61 b, or 62 orthe like, are light-transmitting films. FIG. 8B shows separately thetransmission region 30 t that transmits visible light and thelight-blocking region 30 s that blocks visible light that are in thesubpixel 50 of FIG. 8A. A region that does not overlap with any wiringis the transmission region 30 t, as shown in FIG. 8B.

As a comparative example, a subpixel 50 a having a transistor includingpart of the wiring 51, part of the wiring 52, and part of the wiring 59is shown in FIGS. 9A and 9B.

The subpixel 50 a includes transistors 61 c, 61 d, and 62 a. Thetransistors 61 c, 61 d, and 62 a each include two gates with asemiconductor layer therebetween. FIG. 9A also shows the pixel electrode64 and the display region 22.

The transistor 62 a in FIG. 9A has a stacked-layer structure similar tothat of the transistor 62 in FIG. 7A.

The transistor 61 c includes the semiconductor layer 55 over the wiring51, the conductive layer 58 over the semiconductor layer 55, part of thewiring 59, and the like. The transistor 61 d includes the semiconductorlayer 55 over the wiring 51, the conductive layer 58 over thesemiconductor layer 55, part of the wiring 52, and the like.

In the transistor 62 a, conductive layers (not illustrated) serving asthe gate electrode, the source electrode, and the drain electrode have alight-blocking property. FIG. 9B shows separately the transmissionregion 30 t that transmits visible light and the light-blocking region30 s that blocks visible light that are in the subpixel 50 a of FIG. 9A.A region that overlaps with no wiring is the transmission region 30 t,as shown in FIG. 9B.

When the structure of the subpixel 50 a in FIGS. 9A and 9B is employedin a display panel that includes a top-emission light-emitting elementwith a pixel size of 12.75 μm×38.25 μm, a display region diagonaldimension of 13.3 inches, and a definition of 8K, the proportion of thedisplay region 22 in the pixel is 30.1% and the aperture ratio of thepixel (also referred to as the light transmittance) is 11.5%. Incontrast, when the structure of the subpixel 50 in FIGS. 8A and 8B isemployed in such a display panel, the proportion of the display region22 is 30.1% and the light transmittance is 57.6%. The use of the pixellayout shown in FIGS. 8A and 8B improves the light transmittance.

The above is the description of the pixel layout.

The display device of one embodiment of the present invention can switchbetween display only with the light-emitting elements and see-throughdisplay. Accordingly, an electronic device that can change a displaymethod depending on conditions can be obtained. One embodiment of thepresent invention also enables a user to see an extremely brighttransmission image in see-through display.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Embodiment 2

An electronic device including a display device capable of switchingbetween the light-emitting mode and the transmission mode is describedbelow together with a driving method of the display device.

[Structure Example]

FIG. 10 is a block diagram of an electronic device 10 a of oneembodiment of the present invention. The electronic device 10 a includesa control portion 11, an optical sensor 12, the display device 10, adriver portion 13EL, a driver portion 13LC, and the like.

The control portion 11 includes an arithmetic portion 15. The controlportion 11 may further include a memory portion or the like.

The display device 10 includes a display portion 10EL and a transmissioncontrol portion 10LC. The display portion 10EL includes the plurality oflight-emitting elements 90 arranged in matrix. The transmission controlportion 10LC includes the liquid crystal element 40 across the displayregion. Although one liquid crystal element 40 is used in this example,a plurality of liquid crystal elements 40 may be used. For convenience,the display portion 10EL is apparently displaced from the transmissioncontrol portion 10LC; however, the liquid crystal element 40 in thetransmission control portion 10LC in fact overlaps with the displayregion of the display portion 10EL.

The driver portion 13EL includes a circuit for driving the displayportion 10EL. Specifically, the driver portion 13EL supplies a signalincluding a gray level, a scan signal, a timing signal, a power supplypotential, and the like to a pixel circuit in the display portion 10EL.The driver portion 13EL includes a signal line driver circuit and a scanline driver circuit, for example.

The driver portion 13LC includes a circuit for driving the transmissioncontrol portion 10LC. The driver portion 13LC supplies a signalincluding a gray level, a power supply potential, and the like to theliquid crystal element 40, for example. The driver portion 13LC maysupply a scan signal, a timing signal, and the like when the liquidcrystal element 40 in the transmission portion 10LC is, for example, apassive matrix liquid crystal element or an active matrix liquid crystalelement.

The optical sensor 12 has a function of capturing an image of thebackground behind the display device 10 (the view on the back sideopposite to the display surface side). The optical sensor 12 can outputa signal L0 including data of a captured image in response torequirement by the arithmetic portion 15.

An image signal S0 including image data is input to the arithmeticportion 15 in the control portion 11 from the outside. The arithmeticportion 15 generates a signal 51 from the image signal S0 and outputsthe signal 51 to the driver portion 13EL. The signal 51 includes a graylevel to be supplied to a pixel in the display portion 10EL.

The arithmetic portion 15 also generates a signal S2 and outputs thesignal S2 to the driver portion 13LC. The signal S2 includes a graylevel corresponding to the transmittance of the transmission controlportion 10LC.

The arithmetic portion 15 chooses between the transmission state and thenon-transmission state of the transmission control portion 10LC inaccordance with, for example, an input by a user or an instruction by arunning application, and outputs the signal S2 to the driver portion13LC. The arithmetic portion 15 can perform switching from thetransmission state to the non-transmission state or from thenon-transmission state to the transmission state.

The arithmetic portion 15 can analyze the image data in the signal L0input from the optical sensor 12, and choose between the transmissionstate and the non-transmission state of the transmission control portion10LC on the basis of the analysis result.

For example, while the transmission control portion 10LC is in thenon-transmission state, the arithmetic portion 15 determines whetherthere is a danger around a user. If recognizing a danger, the arithmeticportion 15 switches the state of the transmission control portion 10LCto the transmission state.

Examples of a danger around a user include approach of an object (e.g.,a moving object such as a vehicle or an automobile, a pedestrian, or aball) to the user and existence of an obstacle or a step in user's way.

Specifically, the arithmetic portion 15 can calculate a distance fromthe user or the electronic device 10 a to the object on the basis of theimage data input from the optical sensor 12. In addition, the arithmeticportion 15 can calculate the relative speeds of the object and the useror the electronic device 10 a, the moving direction of the object, orthe like, by analyzing a plurality of image data captured at certaintime intervals (i.e., a moving image). Accordingly, the arithmeticportion 15 can also predict the risk of contact of the user with theobject.

In particular, if a user is immersed in looking and listening with awearable (e.g., glasses-type or goggle-type) electronic device or aportable information terminal such as a smartphone or a tablet terminal,the user may fail to notice a danger around the user. Switching of thedisplay state to the transmission mode allows the user to notice theimminent danger. The user can see the situation ahead through theelectronic device 10 a and thus does not need to move the electronicdevice 10 a to the outside of user's sight; accordingly, the user cannotice the danger quickly.

For example, a bicycle is approaching a user who wears and uses thegoggle-type electronic device 10 a in the light-emitting mode, as shownin FIG. 11A1. In FIG. 11A1, the user is sufficiently distant from thebicycle. When the bicycle approaches the user from the point in FIG.11A1 as shown in FIG. 11A2, the display device 10 switches from thelight-emitting mode to the transmission mode so that the user can seethe bicycle through the electronic device 10 a; as a result, the usercan take an evasive action immediately.

FIGS. 11B1 and 11B2 show an example where the user uses the electronicdevice 10 a in tablet form. The user enjoys looking and listening withthe electronic device 10 a in the light-emitting mode while walking.Switching of the display device 10 from the light-emitting mode to thetransmission mode allows the user to see a bicycle through theelectronic device 10 a. Thus, the user can take an evasive actionimmediately.

[Operation Example]

An example of operation of the display device 10 that can be executed bythe electronic device 10 a is described blow. Here, an example ofswitching of the display state from the non-transmission mode to thetransmission mode is described. FIG. 12 is a flow chart relating tooperation of the arithmetic portion 15.

In Step S11, display in non-transmission mode (emission mode) isperformed.

In Step S12, the arithmetic portion 15 starts to require the opticalsensor 12 to obtain data. The optical sensor 12 outputs, to thearithmetic portion 15, a signal including data of a captured image ofthe environment around a user. The requirement is continually performeduntil the operation is terminated.

More frequent image data acquisition by the optical sensor 12 leads tomore accurate condition assessment. For example, the frequency of dataacquisition in Step S12 is set to once or more every five seconds,preferably once or more per second, more preferably twice or more persecond, further preferably five times or more per second, and 60 timesor less per second or 120 times or less per second.

In Step S13, the arithmetic portion 15 analyzes the image data anddetermines whether there is a danger around a user. Recognition of adanger triggers a shift to Step S14, while recognition of no dangertriggers a return to Step S11 so that the display device continuesdisplay in non-transmission mode.

In Step S14, switched from the non-transmission mode, the display deviceperforms display in the transmission mode.

Instantaneous switching (e.g., switching in a period less than 50 ms)from the non-transmission mode to the transmission mode can give a usera sufficient time for evading the danger. Alternatively, to prevent auser from being surprised at fast switching, switching from thenon-transmission mode to the transmission mode can be performed in sucha manner that the transmittance is continuously changed in a period longenough to allow the user to perceive the gradual change. For example, aperiod for switching from the non-transmission mode to the transmissionmode can be 0.1 seconds or longer, 0.5 seconds or longer, or 1 second orlonger, and 5 seconds or shorter, or preferably 2 seconds or shorter.

Before or in a period for switching from the non-transmission mode tothe transmission mode, information that gives the user a notice ofrecognized danger is preferably displayed on the display device 10.

In Step S15, the arithmetic portion 15 analyzes the image data anddetermines whether the danger around the user still exists. Recognitionof the continuous existence of the danger triggers a return to Step S14so that the display device continues the display in the transmissionmode. The elimination of the danger triggers a shift to Step S16.

In Step S16, decision whether the display is continued is made. Decisionto continue the display triggers a return to Step S11 to perform displayin non-transmission mode. Decision not to continue the display triggersa termination of the display.

The above is the description of the operation example of the electronicdevice 10 a.

[Example of Wearable Electronic Device]

More specific examples of the electronic device of one embodiment of thepresent invention are described below. Here, a goggle-type image displaydevice is given as an example.

FIGS. 13A1 and 13A2 are perspective views of an image display device100. FIG. 13A1 is a perspective view illustrating the front surface, thetop surface, and the left side surface of the image display device 100,and FIG. 13A2 is a perspective view illustrating the back surface, thebottom surface, and the right side surface of the image display device100.

The image display device 100 includes a housing 101, a display portion102, a camera 103, and a mounting fixture 104. The display portion 102includes the above-described display device.

FIG. 13A1 shows the image display device 100 in the light-emitting modein which the display portion 102 is in a state of blocking visiblelight. FIG. 13B shows the image display device 100 in the see-throughmode in which the display portion 102 is in a state of transmittingvisible light. In FIG. 13B, a portion behind the display portion 102that can be seen through the display portion 102 is shown by dashedlines.

FIGS. 13C and 13D are schematic cross-sectional views taken along aplane parallel to the top surface of the image display device 100. Aportion corresponding to the display portion 102 includes a displaypanel 102 p and a protective component 101 t. The protective component101 t transmits visible light and has a function of protecting thedisplay panel 102 p.

FIG. 13C shows the image display device in the emission mode in whichthe display panel 102 p is in a state of blocking visible light. A usercan see an image displayed with the light 20 e emitted from the displaypanel 102 p. FIG. 13D shows the image display device in the see-throughmode in which the display panel 102 p is in a state of transmittingexternal light. The user can see both the light 20 e and thetransmission light 20 t.

FIGS. 14A and 14B illustrate an image display device 100 a that has astructure partly different from the above. FIGS. 14C and 14D illustrateschematic cross-sectional views of the image display device 100 a.

The image display device 100 a includes a shutter 102LC and a pair ofdisplay panels 102EL. A pair of lenses (a lens 105 a and a lens 105 b)is positioned with the display panel 102EL therebetween.

The shutter 102LC corresponds to the above-mentioned transmissioncontrol portion 10LC. The display panel 102EL corresponds to theabove-mentioned display portion 10EL; the display panel 102EL is adisplay device including a plurality of light-emitting elements arrangedin matrix and a portion transmitting visible light.

The lens 105 b that is closer to a user than the other lens is has afunction of making user's eyes focus on the display panel 102EL. Thiscan reduce a distance between user's eye and the display panel 102EL,decreasing the thickness of the image display device 100 a.

In the see-through mode, light transmitted through the shutter 102LCgoes through the display panel 102EL and the two lenses, between whichthe display panel 102EL is located, and then reaches user's eye. Thus,the user can see a clear transmission image. For example, when thedisplay panel 102EL is a high-definition display panel, lighttransmitted through the display panel 102EL may be diffracted because ofperiodically arranged pixels. However, the pair of lenses between whichthe display panel is sandwiched can eliminate the influence ofdiffraction.

When the two lenses are convex lenses with the same focal length, atransmission image can be seen at the same magnification. To prevent theinversion of a transmission image, another kind of lenses may beprovided.

The two convex lenses are provided with the display panel 102ELtherebetween in this example; however, not limited to such lenses, avariety of optical systems is available. An optical system with amicrolens array, a mirror surface, or the like may be used instead ofthe lenses.

The display panel 102EL for the right eye and that for the left eye areprovided in this example; however, one display panel 102EL alone may beused. The display panel 102EL may be held in a state of being bent.

FIGS. 14E1 and 14E2 illustrate an example where the shutter 102LC isprovided also on the top surface and the bottom surface of the housing101. The display portion 102 shown in FIG. 13A1 or the like may beemployed for a portion where the shutter 102LC is provided. Such astructure can widen the viewing angle in the upward and downwarddirections in the see-through mode.

The above is the description of the electronic device.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Embodiment 3

In this embodiment, structure examples of the display device (displaypanel) of one embodiment of the present invention are described withreference to drawings.

[Structure Example of Display Panel]

FIG. 15 is a schematic perspective view illustrating a display panel 300of one embodiment of the present invention. In the display panel 300, asubstrate 351 and a substrate 361 are attached to each other. In FIG.15, the substrate 351 is denoted by a dashed line.

The display panel 300 includes a display portion 362, a circuit 364, awiring 365, and the like. The circuit 364, the wiring 365, and the likeare between the substrates 351 and 361. FIG. 15 shows an example inwhich an IC 373 and an FPC 372 are mounted on the substrate 351. Thus,the structure illustrated in FIG. 15 can be referred to as a displaymodule including the display panel 300, the FPC 372, and the IC 373.

As the circuit 364, for example, a circuit functioning as a scan linedriver circuit can be used.

The wiring 365 has a function of supplying a signal or electric power tothe display portion or the circuit 364. The signal or electric power isinput to the wiring 365 from the outside through the FPC 372 or from theIC 373.

FIG. 15 shows an example in which the IC 373 is provided on thesubstrate 351 by a chip on glass (COG) method or the like. As the IC373, an IC functioning as a scan line driver circuit, a signal linedriver circuit, or the like can be used. Note that the IC 373 may beomitted when, for example, the display panel 300 includes circuitsfunctioning as a scan line driver circuit and a signal line drivercircuit or when circuits functioning as a scan line driver circuit and asignal line driver circuit are externally provided and signals fordriving the display panel 300 are input through the FPC 372.Alternatively, the IC 373 may be mounted on the FPC 372 by a chip onfilm (COF) method or the like.

FIG. 15 also illustrates an enlarged view of part of the display portion362. A plurality of light-emitting elements 360 are arranged in matrixin the display portion 362. The liquid crystal element 340 is providedin a portion where the plurality of light-emitting elements 360 are notprovided.

When serving as a touch panel, the display panel 300 can include a touchsensor 366 over the substrate 361. For example, a sheet-like capacitivetouch sensor 366 may be provided to overlap with the display portion362. Alternatively, a touch sensor may be provided between the substrate361 and the substrate 351. For a touch sensor provided between thesubstrate 361 and the substrate 351, a capacitive touch sensor or anoptical touch sensor using a photoelectric conversion element may beused.

CROSS-SECTIONAL STRUCTURE EXAMPLES

An example of a cross-sectional structure of the display panel isdescribed below.

Cross-Sectional Structure Example 1

FIG. 16A shows an example of cross sections of part of a regionincluding the FPC 372, part of a region including the circuit 364, andpart of a region including the display portion 362 of the display panelillustrated as an example in FIG. 15. Note that the touch sensor 366 isnot illustrated.

The display panel 300 includes an insulating layer 220 between thesubstrates 351 and 361. The display panel also includes thelight-emitting element 360, a transistor 201, a transistor 202, atransistor 205, a wiring 209, a coloring layer 134, and the like betweenthe substrate 351 and the insulating layer 220. Furthermore, the displaypanel includes the liquid crystal element 340 and the like between theinsulating layer 220 and the substrate 361. The substrate 361 and theinsulating layer 220 are bonded with an adhesive layer 161. Thesubstrate 351 and the insulating layer 220 are bonded with an adhesivelayer 162.

The wiring 209 is electrically connected to the liquid crystal element340. The transistor 205 is electrically connected to the light-emittingelement 360. The transistor 205 and the wiring 209 are formed on asurface of the insulating layer 220 that is on the substrate 351 side,whereby the transistor 205 and the wiring 209 can be formed through thesame process.

The wiring 209, a connection portion 207, or the like is preferablyprovided outside the display portion 362. When a plurality of liquidcrystal elements 340 are used, the connection portion 207 or the wiring209 for the liquid crystal element 340 positioned in contact with an endportion of the display portion 362 can be outside the display portion362. The connection portion 207 or the wiring 209 for the liquid crystalelement 340 in a portion other than the end portion of the displayportion 362 may be inside the display portion 362.

A conductive layer 313 serving as a common electrode of the liquidcrystal element 340, an alignment film 133 b, an insulating layer 117,and the like are provided over the substrate 361. The insulating layer117 serves as a spacer for holding a cell gap of the liquid crystalelement 340.

Insulating layers such as an insulating layer 211, an insulating layer212, an insulating layer 213, an insulating layer 214, and an insulatinglayer 215 are provided on the substrate 351 side of the insulating layer220. Parts of the insulating layer 211 function as gate insulatinglayers of the transistors. The insulating layer 212, the insulatinglayer 213, and the insulating layer 214 are provided to cover thetransistors. The insulating layer 215 is provided to cover theinsulating layer 214. The insulating layers 214 and 215 each function asa planarization layer. Note that the three insulating layers, theinsulating layers 212, 213, and 214, are provided to cover thetransistors and the like in this example; however, the number ofinsulating layers is not limited to three, and four or more insulatinglayers, a single insulating layer, or two insulating layers may beprovided. The insulating layer 214 functioning as a planarization layeris not necessarily provided when not needed.

FIG. 16A illustrates the circuit 364 in which the transistor 201 isprovided, as an example of the circuit 364.

FIGS. 16B and 16C are enlarged views of the transistor 205 and thetransistor 201, respectively.

The transistor 205 includes a conductive layer 221 t serving as a gateelectrode, an insulating layer 211 over the conductive layer 221 t, asemiconductor layer 231 over the insulating layer 211, a pair ofconductive layers 222 t serving as a source electrode and a drainelectrode, a conductive layer 223 overlapping with the semiconductorlayer 231 with the insulating layer 212 therebetween. The conductivelayer 221 t, the semiconductor layer 231, the conductive layers 222 t,and the conductive layer 223 are each a film that transmits visiblelight. Accordingly, the transistor 205 can transmit visible light.

The transistor 202 is the same as the transistor 205 except that theconductive layer 223 serving as one of gate electrodes is not included.Thus, the transistor 202 can also transmit visible light.

The transistor 201 includes a conductive layer 221 serving as a gateelectrode, the insulating layer 211 over the conductive layer 221, thesemiconductor layer 231 over the insulating layer 211, a pair ofconductive layers 222 serving as a source electrode and a drainelectrode, the conductive layer 223 overlapping with the semiconductorlayer 231 with the insulating layer 212 therebetween. Here, theconductive layers 221 and 222 are each preferably a film that blocksvisible light.

FIG. 16D shows an example where the conductive layers 221, 221 t, 222,and 222 t are connected to each other. No insulating layer is providedbetween the conductive layers 221 and 221 t; the conductive layer 221 isstacked partly on and connected to the conductive layer 221 t. Theconductive layers 221 and 222 t are connected to each other in anopening provided in the insulating layer 211. No insulating layer isprovided between the conductive layers 222 t and 222; the conductivelayer 222 is stacked partly on and connected to the conductive layer 222t.

The structure of the connection portion shown in FIG. 16D is an examplefor facilitating description, and other structures are also available.For example, the conductive layers 221 t and 222, or the conductivelayers 221 t and 222 t, are electrically connected to each other in anopening provided in the insulating layer 211.

The stacking order of the conductive layers 221 and 221 t may bereversed. Similarly, the stacking order of the conductive layers 222 and222 t may be reversed.

The semiconductor layer 231 in each of the transistors can be formedwith a light-transmitting semiconductor material. Examples of thelight-transmitting semiconductor material include an oxidesemiconductor. The oxide semiconductor preferably contains at leastindium. In particular, indium and zinc are preferably contained. Inaddition, one or more kinds of elements selected from aluminum, gallium,yttrium, copper, vanadium, beryllium, boron, silicon, titanium, iron,nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium,hafnium, tantalum, tungsten, magnesium, and the like may be contained.

The conductive films included in the light-transmitting transistors eachcan be formed using a light-transmitting conductive material. Thelight-transmitting conductive material preferably contains one or morekinds of indium, zinc, and tin. Specifically, an In oxide, an In—Snoxide (also referred to as an indium tin oxide or ITO), an In—Zn oxide,an In—W oxide, an In—W—Zn oxide, an In—Ti oxide, an In—Sn—Ti oxide, anIn—Sn—Si oxide, a Zn oxide, a Ga—Zn oxide, or the like can be used.

Any of the conductive films of the light-transmitting transistor may bean oxide semiconductor that includes an impurity element, for example,and has reduced resistance. The oxide semiconductor with the reducedresistance can be regarded as an oxide conductor (OC).

For example, to form an oxide conductor, oxygen vacancies are formed inan oxide semiconductor and then hydrogen is added to the oxygenvacancies, so that a donor level is formed in the vicinity of theconduction band. The oxide semiconductor having the donor level has anincreased conductivity and becomes a conductor.

An oxide semiconductor has a large energy gap (e.g., an energy gap of2.5 eV or larger), and thus has a visible-light-transmitting property.An oxide conductor is an oxide semiconductor having a donor level in thevicinity of the conduction band, as described above. Therefore, theinfluence of absorption due to the donor level is small in an oxideconductor, and an oxide conductor has a visible-light-transmittingproperty comparable to that of an oxide semiconductor.

The oxide conductor preferably includes one or more kinds of metalelements included in the semiconductor film of the transistor. When twoor more layers included in the transistor are formed using oxidesemiconductors including the same metal element, the same manufacturingapparatus (e.g., deposition apparatus or processing apparatus) can beused in two or more steps and manufacturing cost can thus be reduced.

The liquid crystal element 340 is a transmissive liquid crystal element.The liquid crystal element 340 has a structure in which a conductivelayer 311, a liquid crystal 312, and the conductive layer 313 arestacked. The conductive layers 311 and 313 each contain a materialtransmitting visible light. In addition, an alignment film 133 a isprovided between the liquid crystal 312 and the conductive layer 311,and the alignment film 133 b is provided between the liquid crystal 312and the conductive layer 313. A polarizing plate 130 b is provided on anouter surface of the substrate 361. A polarizing plate 130 a is providedon an outer surface of the substrate 351.

In the liquid crystal element 340, the conductive layer 311 and theconductive layer 313 have a function of transmitting visible light.Light entering from the substrate 361 side is polarized by thepolarizing plate 130 b, is transmitted through the conductive layer 311,the liquid crystal 312, the conductive layer 313, and the like, andreaches the polarizing plate 130 a. Here, the alignment of the liquidcrystal is controlled by a voltage applied between the conductive layer311 and the conductive layer 313, whereby optical modulation of lightcan be controlled. That is, the intensity of light casted through thepolarizing plate 130 a can be controlled.

Light transmitted through the liquid crystal element 340 can be seenfrom the substrate 351 side through the transistor 205, the transistor202, the light-emitting element 360, and the like, each of which cantransmit visible light.

Depending on the structure of the liquid crystal element 340, one orboth of the polarizing plates 130 a and 130 b may be omitted. Forexample, the use of a guest-host liquid crystal element as the liquidcrystal element 340 can eliminate the polarizing plate 130 a. This canincrease the light extraction efficiency of the light-emitting element360.

The light-emitting element 360 is a dual-emission light-emittingelement. The light-emitting element 360 has a structure in which aconductive layer 191, an EL layer 192, and a conductive layer 193 arestacked in this order from the insulating layer 220 side. An insulatinglayer 194 is provided to cover the conductive layer 193. The conductivelayers 191 and 193 each contain a material transmitting visible light.Part of light emitted from the light-emitting element 360 goes outsidethrough the coloring layer 134, the substrate 351, and the like.

Since the light-emitting element 360 is a dual-emission light-emittingelement, a region where the light-emitting element 360 is provided canalso be used as the transmission region. Note that when the definitionis low (e.g., lower than 100 ppi) or when the transmission region otherthan the light-emitting element 360 is sufficiently large, thelight-emitting element 360 may be a top-emission light-emitting element.In that case, the conductive layer 193 can be formed using a materialreflecting visible light and thus the light extraction efficiency of thelight-emitting element 360 can be increased.

As the polarizing plate 130 a provided on the outer surface of thesubstrate 351, a linear polarizing plate or a circularly polarizingplate can be used. An example of a circularly polarizing plate is astack including a linear polarizing plate and a quarter-wave retardationplate. Such a structure can reduce reflection of external light. A lightdiffusion plate may be provided to reduce reflection of external light.The cell gap, orientation, drive voltage, and the like of the liquidcrystal element used as the liquid crystal element 340 are adjusteddepending on the kind of the polarizing plate so that desirable contrastis obtained.

An insulating layer 217 is provided over the insulating layer 216 thatcovers an end portion of the conductive layer 191. The insulating layer217 has a function as a spacer for preventing the insulating layer 220and the substrate 351 from getting closer than necessary. In addition,in the case where the EL layer 192 or the conductive layer 193 is formedusing a shielding mask (metal mask), the insulating layer 217 mask mayhave a function of preventing the shielding mask from being in contactwith a surface on which the EL layer 192 or the conductive layer 193 isformed. Note that the insulating layer 217 is not necessarily providedwhen not needed.

One of a source and a drain of the transistor 205 is electricallyconnected to the conductive layer 191 of the light-emitting element 360through a conductive layer 224.

The wiring 209 is electrically connected to the conductive layer 311through the connection portion 207. The connection portion 207 is aportion in which the conductive layers provided on both surfaces of theinsulating layer 220 are connected to each other in an opening providedin the insulating layer 220.

A connection portion 204 is provided in a region near an end portion ofthe substrate 351. The connection portion 204 is electrically connectedto the FPC 372 through a connection layer 242. The connection portion204 has a structure similar to that of the connection portion 207. Onthe bottom surface of the connection portion 204, a conductive layerobtained by processing a conductive film that is also used to form theconductive layer 311 is exposed. Thus, the connection portion 204 andthe FPC 372 can be electrically connected to each other through theconnection layer 242.

A connection portion 252 is provided in part of a region where theadhesive layer 161 is provided. In the connection portion 252, theconductive layer obtained by processing a conductive film that is alsoused to form the conductive layer 311 is electrically connected to partof the conductive layer 313 with a connector 243. Accordingly, a signalor a potential input from the FPC 372 connected to the substrate 351side can be supplied to the conductive layer 313 formed on the substrate361 side through the connection portion 252.

As the connector 243, a conductive particle can be used, for example. Asthe conductive particle, a particle of an organic resin, silica, or thelike coated with a metal material can be used. Nickel or gold, which canreduce contact resistance, is preferably used as the metal material. Itis also preferable to use a particle coated with layers of two or morekinds of metal materials, such as a particle coated with nickel andfurther with gold. As the connector 243, a material capable of elasticdeformation or plastic deformation is preferably used. As illustrated inFIG. 16A, the connector 243 that is the conductive particle has avertically crushed shape in some cases. The crushed shape leads to anincrease in the contact area between the connector 243 and a conductivelayer electrically connected to the connector 243, thereby reducingcontact resistance and suppressing the generation of problems such asdisconnection.

The connector 243 is preferably provided so as to be covered with theadhesive layer 161. For example, the connector 243 is dispersed in theadhesive layer 161 that is not yet cured.

In the example of FIG. 16A, the transistors 201 and 205 each have astructure in which the semiconductor layer 231 where a channel is formedis provided between two gates. One gate is formed by the conductivelayer 221 and the other gate is formed by a conductive layer 223overlapping with the semiconductor layer 231 with the insulating layer212 therebetween. Such a structure enables control of threshold voltagesof transistors. Here, the two gate electrodes may be connected to eachother and supplied with the same signal to operate the transistors. Suchtransistors can have a higher field-effect mobility and thus have ahigher on-state current than other transistors. Consequently, a circuitcapable of high-speed operation can be obtained. Furthermore, the areaoccupied by a circuit portion can be reduced. The use of the transistorhaving a high on-state current can reduce signal delay in wirings andcan reduce display unevenness even in a display panel in which thenumber of wirings is increased because of increase in size ordefinition.

Note that the transistor included in the circuit 364 and the transistorincluded in the display portion 362 may have the same structure. Aplurality of transistors included in the circuit 364 may have the samestructure or different structures. A plurality of transistors includedin the display portion 362 may have the same structure or differentstructures.

A material through which impurities such as water or hydrogen do noteasily diffuse is preferably used for at least one of the insulatinglayers 212 and 213 that cover the transistors. That is, the insulatinglayer 212 or the insulating layer 213 can function as a barrier film.Such a structure can effectively suppress diffusion of the impuritiesinto the transistors from the outside, allowing the display panel tohave high reliability.

Cross-Sectional Structure Example 2

FIG. 17 shows an example including a transistor 206 electricallyconnected to the liquid crystal element 340. The transistor 206 servesas a selection transistor for the liquid crystal element 340.Accordingly, the liquid crystal element 340 can be an active matrixliquid crystal element.

The transistor 206 includes the conductive layers 221 t and 222 t andthe like that have a light-transmitting property, like the transistor202. Thus, a region where the transistor 206 is provided serves as thetransmission region.

In the connection portion 207, the conductive layer 221 t and part ofthe conductive layer 222 t serving as one of a source and a drain of thetransistor 206 are in contact with each other. Thus, the conductivelayer 311 of the liquid crystal element 340 is electrically connected tothe transistor 206 through the connection portion 207. A region wherethe connection portion 207 is provided also serves as the transmissionregion.

When the semiconductor layer 231 of the transistor 206 includes an oxidesemiconductor, the liquid crystal element 340 can be driven at a lowframe frequency (e.g., lower than 1 Hz). This enables a reduction inpower consumption at the time of driving the liquid crystal element 340.

Cross-Sectional Structure Example 3

FIG. 18 shows an example of a structure in which the transistors 201,202, and 205 have structures different from those shown in FIG. 16A andthe like.

The transistor 202 is a top-gate transistor. Each of the transistors 201and 205 has the same structure as the transistor 202 except to furtherinclude a conductive layer serving as a second gate.

Conductive layers serving as gate electrodes, source electrodes, anddrain electrodes of the transistors 202 and 205 are each preferably aconductive film that transmits visible light. In that case, a regionwhere the transistors 202 and 205 are provided can be the transmissionregion.

In contrast, conductive layers serving as a gate electrode, a sourceelectrode, and a drain electrode of the transistor 201 can each be aconductive film that blocks visible light.

Cross-Sectional Structure Example 4

The display panel of one embodiment of the present invention may includea region where the transistor 205 and the transistor 208, which areprovided in a pixel, overlap with each other as illustrated in FIG. 19.The display device with such a structure can have a reduced area perpixel and a high pixel density and can display a high definition image.

The display panel with such a structure can have a high definition over1,500 ppi or 2,000 ppi, even when formed with a glass substrate or thelike.

One of a source and a drain of the transistor 208 serves as one gate ofthe transistor 205.

For example, the display panel can include a region where the transistor205 for driving the light-emitting element 360 and the transistor 208overlap with each other. When the liquid crystal element 340 includes anactive matrix transistor, the display panel may include a region wherethe transistor for driving the liquid crystal element 340 and one of thetransistors 205 and 208 overlap with each other.

Conductive layers serving as gate electrodes, source electrodes, anddrain electrodes of the transistors 208 and 205 are each preferably alight-transmitting conductive film.

Cross-Sectional Structure Example 5

In the above structure, the light-emitting element 360 and the liquidcrystal element 340 between which the insulating layer 220 is locatedare between the pair of substrates; however, other structures are alsoavailable. For example, a light-emitting panel including thelight-emitting element 360 and a pair of substrates may be attached to aliquid crystal panel including the liquid crystal element 340 and a pairof substrates. FIG. 20 illustrates such an example.

In FIG. 20, the liquid crystal element 340 is between a substrate 361 aand a substrate 361 b. The light-emitting element 360, the transistors201, 202, and 205, and the like are between a substrate 351 a and asubstrate 351 b. The structure including the substrates 351 a and 351 bis referred to as a light-emitting panel, and the structure includingthe substrates 361 a and 361 b is referred to as a liquid crystal panel.

The substrates 361 b and 351 a are attached to each other with anadhesive layer 352. The adhesive layer 352 has a light-transmittingproperty. For example, a sheet-like or film-like adhesive can be used.For example, an optical clear adhesive (OCA) film is preferably used.

In such a structure, the polarizing plate 130 a can be positionedbetween the substrate 351 a and the substrate 361 b. Accordingly, thelight extraction efficiency of the light-emitting element 360 can beincreased and bright display can be performed with low powerconsumption.

Such a structure enables separate formation of the light-emitting paneland the liquid crystal panel and later attachment thereof. This canimprove the yield. It is preferable that the liquid crystal element 340be a passive matrix liquid crystal element or a segment liquid crystalelement and be large enough to cover a plurality of light-emittingelements 360. In that case, high positional accuracy is not required inattachment of the light-emitting panel and the liquid crystal panel,whereby the productivity can be improved.

[Example of Manufacturing Method]

As an example of a method for manufacturing a display device of oneembodiment of the present invention, a method for manufacturing thedisplay device shown in FIG. 16A and the like is described below.

Over a support substrate, the conductive layer 311 is formed andsubsequently the insulating layer 220 is formed. After that, thetransistors 201, 202, and 205, the light-emitting element 360, and thelike are formed over the insulating layer 220. Here, an opening reachingthe conductive layer 311 is formed in the insulating layer 220, and theconductive layer 221 and the like are formed to cover the opening; as aresult, the connection portion 207 is formed.

The conductive layers 221 t and 221 are formed in the following manner.A conductive film to be the conductive layer 221 t is formed, theconductive film is etched with the use of a resist mask over theconductive film, and then the resist mask is removed; as a result, theconductive layer 221 t is formed. Next, a conductive film covering theconductive layer 221 t is formed, and the conductive film is etched withthe use of a resist mask; as a result, the conductive layer 221 isformed. The conductive layer 221 is preferably etched under a conditionthat does not cause, or hardly causes, etching of the conductive layer221 t. The conductive layers 222 and 222 t can be formed in a similarmanner.

Next, the substrate 351 and the support substrate are attached to eachother with the adhesive layer 162. After that, the support substrate isseparated from the conductive layer 311 and the insulating layer 220.

For separation of the support substrate from the conductive layer 311and the insulating layer 220, a separation layer is provided between thesupport substrate and two of the conductive layer 311 and the insulatinglayer 220. The separation layer has a structure that allows separationbetween the separation layer and the support substrate, in theseparation layer, or between the separation layer and the conductivelayer 311 or the insulation layer 220.

For example, as the separation layer, it is possible to use a stack of alayer containing a high-melting-point metal material such as tungstenand a layer containing an oxide of the metal material. As the insulatinglayer over the separation layer, it is possible to use an insulatinglayer containing an inorganic insulating material such as siliconnitride, silicon oxide, silicon oxynitride, or silicon nitride oxide. Inthat case, separation can be caused at the interface between tungstenand tungsten oxide, in tungsten oxide, or at the interface betweentungsten oxide and the insulating layer.

Alternatively, an organic resin may be used for the separation layer sothat separation can be caused at the interface between the supportsubstrate and the separation layer, in the separation layer, or at theinterface between the separation layer and the insulating layer over theseparation layer.

Typically, a polyimide resin can be used for the organic resin. Thepolyimide resin is preferable because of its high heat resistance. Anacrylic resin, an epoxy resin, a polyamide resin, a polyimide-amideresin, a siloxane resin, a benzocyclobutene-based resin, a phenol resin,or the like can also be used. For example, to form the organic resin, amixed material of a resin precursor and a solvent is formed over thesupport substrate by a method such as spin coating, dipping, spraycoating, inkjet printing, dispensing, screen printing, or offsetprinting, or with a doctor knife, a slit coater, a roll coater, acurtain coater, or a knife coater. After that, heat treatment isperformed to remove the solvent and the like and cure the material, sothat the separation layer containing the organic resin can be formed.

For example, a resin precursor that can generate an imide bond bydehydration can be used to prepare polyimide. Alternatively, a materialcontaining a soluble polyimide resin may be used.

The organic resin may be either photosensitive or nonphotosensitive. Aphotosensitive polyimide is a material that is suitably used for aplanarization film or the like of the display panel, and therefore, theformation apparatus and the material can be shared. Thus, there is noneed to prepare another apparatus and another material to obtain thestructure of one embodiment of the present invention. Furthermore, theseparation layer that is formed using a photosensitive resin materialcan be processed by light exposure and development treatment.

For example, an opening portion can be formed and an unnecessary portioncan be removed. Moreover, by optimizing a light exposure method or lightexposure conditions, an uneven shape can be formed in a surface of theresin layer. For example, a multiple exposure technique or an exposuretechnique using a half-tone mask or a gray-tone mask may be used.

When the separation layer is heated locally, the separability can beimproved in some cases. For example, the separation layer can beirradiated with laser light. It is preferable to perform the irradiationby scanning using linear laser light. Such irradiation can shorten theprocess time in the case of using a large support substrate. As thelaser light, excimer laser light with a wavelength of 308 nm can besuitably used.

When light irradiation with laser light or the like is to be performedto improve the separability, a heat generation layer may be provided tooverlap with the separation layer. The heat generation layer has afunction of generating heat by absorbing light. The heat generationlayer is preferably provided between the support substrate and theseparation layer, but may be provided over the separation layer. Amaterial that can absorb part of light used as laser light or the likecan be used for the heat generation layer. For example, a metal, anoxide, or the like can be included in the heat generation layer whenexcimer laser light with a wavelength of 308 nm is used as the laserlight. For example, a metal such as titanium or tungsten, an oxideconductive material such as titanium oxide, tungsten oxide, indiumoxide, or indium tin oxide, or an indium-containing oxide semiconductormaterial can be used.

In some cases, part of the separation layer remains on the light path inthe light-emitting element 360 or the liquid crystal element 340 afterthe separation. In the case where the separation layer absorbs part ofvisible light, light transmitted through the separation layer might becolored. For this reason, after the separation, the remaining separationlayer is preferably removed by etching. For example, in the case wherean organic resin is used for the separation layer, the remainingseparation layer can be removed by, for example, plasma treatment (alsoreferred to as ashing treatment) in an oxygen-containing atmosphere.

When a surface of the conductive layer 311 is exposed by treatment suchas etching after the separation, an electric field can be moreefficiently applied to the liquid crystal element 340 and the drivingvoltage can thus be reduced. When an insulating film through whichimpurities such as water hardly diffuse (e.g., a film containing aninorganic insulating material such as silicon oxide, silicon nitride, oraluminum oxide) remains on the surface of the conductive layer 311 afterthe separation, the remaining insulating film can serve as a protectionfilm that prevents diffusion of impurities into the liquid crystal 312.

After that, the alignment film 133 a is formed over the insulating layer220 and the conductive layer 311. Then, the substrate 351 and thesubstrate 361 where the conductive layer 313, the alignment film 133 b,and the like are already formed are attached to each other with theliquid crystal 312 therebetween.

In the above manner, the display panel 300 shown in FIG. 16A can beformed.

[Components]

The above components will be described below.

[Substrate]

A material having a flat surface can be used as the substrate includedin the display panel. The substrate on the side from which light fromthe display element is extracted is formed using a material thattransmits the light. For example, a material such as glass, quartz,ceramic, sapphire, or an organic resin can be used.

The weight and thickness of the display panel can be decreased by usinga thin substrate. A flexible display panel can be obtained by using asubstrate that is thin enough to have flexibility.

Examples of the material that has flexibility and transmits visiblelight include polyester resins such as polyethylene terephthalate (PET)and polyethylene naphthalate (PEN), a polyacrylonitrile resin, apolyimide resin, a polymethyl methacrylate resin, a polycarbonate (PC)resin, a polyethersulfone (PES) resin, a polyamide resin, a cycloolefinresin, a polystyrene resin, a polyamide imide resin, a polyvinylchloride resin, and a polytetrafluoroethylene (PTFE). In particular, amaterial whose thermal expansion coefficient is low is preferred, andfor example, a polyamide imide resin, a polyimide resin, or PET with athermal expansion coefficient of 30×10⁻⁶/K or less can be suitably used.A substrate in which a glass fiber is impregnated with an organic resinor a substrate whose thermal expansion coefficient is reduced by mixingan organic resin with an inorganic filler can also be used. A substrateusing such a material is lightweight, and thus a display panel usingthis substrate can also be lightweight.

In the case where a fibrous body is included in the above material, ahigh-strength fiber of an organic compound or an inorganic compound isused as the fibrous body. The high-strength fiber is specifically afiber with a high tensile elastic modulus or a fiber with a high Young'smodulus. Typical examples thereof include a polyvinyl alcohol basedfiber, a polyester based fiber, a polyamide based fiber, a polyethylenebased fiber, an aramid based fiber, a polyparaphenylene benzobisoxazolefiber, a glass fiber, and a carbon fiber. As the glass fiber, a glassfiber using E glass, S glass, D glass, Q glass, and the like can begiven. These fibers may be used in a state of a woven or nonwovenfabric, and a structure body in which this fibrous body is impregnatedwith a resin and the resin is cured may be used as the flexiblesubstrate. The structure body including the fibrous body and the resinis preferably used as the flexible substrate, in which case thereliability against breaking due to bending or local pressure can beincreased.

Alternatively, glass or the like that is thin enough to have flexibilitycan be used as the substrate. Alternatively, a composite material whereglass and a resin material are attached to each other with an adhesivelayer may be used.

A hard coat layer (e.g., a silicon nitride layer and an aluminum oxidelayer) by which a surface of a display panel is protected from damage, alayer (e.g., an aramid resin layer) that can disperse pressure, or thelike may be stacked over the flexible substrate. Furthermore, tosuppress a decrease in lifetime of the display element due to moistureand the like, an insulating film with low water permeability may bestacked over the flexible substrate. For example, an inorganicinsulating material such as silicon nitride, silicon oxynitride, siliconnitride oxide, aluminum oxide, or aluminum nitride can be used.

The substrate may be formed by stacking a plurality of layers. The useof a glass layer can improve a barrier property against water and oxygenand thus allow the display panel to have high reliability.

[Transistor]

The transistors each include a conductive layer functioning as the gateelectrode, the semiconductor layer, a conductive layer functioning asthe source electrode, a conductive layer functioning as the drainelectrode, and an insulating layer functioning as the gate insulatinglayer.

Note that there is no particular limitation on the structure of thetransistor included in the display device of one embodiment of thepresent invention. For example, a planar transistor, a staggeredtransistor, or an inverted staggered transistor may be used. A top-gatetransistor or a bottom-gate transistor may be used. Gate electrodes maybe provided above and below a channel.

There is no particular limitation on the crystallinity of asemiconductor material used for the transistors, and an amorphoussemiconductor or a semiconductor having crystallinity (amicrocrystalline semiconductor, a polycrystalline semiconductor, asingle-crystal semiconductor, or a semiconductor partly includingcrystal regions) may be used. A semiconductor having crystallinity ispreferably used, in which case deterioration of the transistorcharacteristics can be suppressed.

As a semiconductor material used for the transistors, a metal oxidewhose energy gap is greater than or equal to 2 eV, preferably greaterthan or equal to 2.5 eV, further preferably greater than or equal to 3eV can be used. A typical example thereof is a metal oxide containingindium, and for example, a CAC-OS described later or the like can beused.

A transistor with a metal oxide having a larger band gap and a lowercarrier density than silicon has a low off-state current; therefore,charges stored in a capacitor that is series-connected to the transistorcan be held for a long time.

The semiconductor layer can be, for example, a film represented by anIn-M-Zn-based oxide that contains indium, zinc, and M (a metal such asaluminum, titanium, gallium, germanium, yttrium, zirconium, lanthanum,cerium, tin, neodymium, or hafnium).

In the case where the metal oxide contained in the semiconductor layercontains an In-M-Zn-based oxide, it is preferable that the atomic ratioof metal elements of a sputtering target used for forming a film of theIn-M-Zn oxide satisfy In M and Zn M. The atomic ratio of metal elementsin such a sputtering target is preferably, for example, In:M:Zn=1:1:1,In:M:Zn=1:1:1.2, In:M:Zn=3:1:2, In:M:Zn=4:2:3, In:M:Zn=4:2:4.1,In:M:Zn=5:1:6, In:M:Zn=5:1:7, or In:M:Zn=5:1:8. Note that the atomicratio of metal elements in the formed oxide semiconductor layer variesfrom the above atomic ratios of metal elements of the sputtering targetsin a range of ±40%.

The bottom-gate transistor described in this embodiment is preferablebecause the use of the bottom-gate transistor can reduce the number ofmanufacturing steps. Here, when a metal oxide, which can be formed at alower temperature than polycrystalline silicon, is used, materials withlow heat resistance can be used for a wiring, an electrode, or asubstrate below the semiconductor layer, so that the range of choices ofmaterials can be widened. For example, an extremely large glasssubstrate can be favorably used.

A metal oxide film with low carrier density is used as the semiconductorlayer. For example, the semiconductor layer can include a metal oxidewhose carrier density is lower than or equal to 1×10¹⁷/cm³, preferablylower than or equal to 1×10¹⁵/cm³, more preferably lower than or equalto 1×10¹³/cm³, still more preferably lower than or equal to 1×10¹¹/cm³,even more preferably lower than 1×10¹⁰/cm³, and higher than or equal to1×10⁻⁹/cm³. Such a metal oxide is referred to as a highly purifiedintrinsic or substantially highly purified intrinsic metal oxide. Themetal oxide has a low impurity concentration and a low density of defectstates and can thus be referred to as a metal oxide having stablecharacteristics.

However, the composition is not limited to those described above, and amaterial having the appropriate composition may be used depending onrequired semiconductor characteristics and electrical characteristics ofthe transistor (e.g., field-effect mobility and threshold voltage). Toobtain the required semiconductor characteristics of the transistor, itis preferable that the carrier density, the impurity concentration, thedefect density, the atomic ratio between a metal element and oxygen, theinteratomic distance, the density, and the like of the semiconductorlayer be set to appropriate values.

When silicon or carbon that is one of elements belonging to Group 14 iscontained in the metal oxide contained in the semiconductor layer,oxygen vacancies are increased in the semiconductor layer, and thesemiconductor layer becomes n-type. Thus, the concentration of siliconor carbon (measured by secondary ion mass spectrometry) in thesemiconductor layer is set to lower than or equal to 2×10¹⁸ atoms/cm³,preferably lower than or equal to 2×10¹⁷ atoms/cm³.

Alkali metal and alkaline earth metal might generate carriers whenbonded to a metal oxide, in which case the off-state current of thetransistor might be increased. Therefore, the concentration of alkalimetal or alkaline earth metal of the semiconductor layer, which ismeasured by secondary ion mass spectrometry, is set to lower than orequal to 1×10¹⁸ atoms/cm³, preferably lower than or equal to 2×10¹⁶atoms/cm³.

When nitrogen is contained in the metal oxide contained in thesemiconductor layer, electrons serving as carriers are generated and thecarrier density increases, so that the semiconductor layer easilybecomes n-type. Thus, a transistor including a metal oxide that containsnitrogen is likely to be normally on. Hence, the concentration ofnitrogen which is measured by secondary ion mass spectrometry ispreferably set to lower than or equal to 5×10¹⁸ atoms/cm³.

An oxide semiconductor is classified into a single-crystal oxidesemiconductor and a non-single-crystal oxide semiconductor. Examples ofa non-single-crystal oxide semiconductor include a c-axis alignedcrystalline oxide semiconductor (CAAC-OS), a polycrystalline oxidesemiconductor, a nanocrystalline oxide semiconductor (nc-OS), anamorphous-like oxide semiconductor (a-like OS), and an amorphous oxidesemiconductor.

The semiconductor layer of any of the transistors disclosed in oneembodiment of the present invention may include a cloud-alignedcomposite OS (CAC-OS).

For the semiconductor layer of any of the transistors disclosed in oneembodiment of the present invention, the above-describednon-single-crystal oxide semiconductor or a CAC-OS can be suitably used.As the non-single-crystal oxide semiconductor, an nc-OS or a CAAC-OS canbe suitably used.

The semiconductor layer of any of the transistors of one embodiment ofthe present invention preferably includes a CAC-OS. The use of a CAC-OScan give the transistor high electrical characteristics or highreliability.

The semiconductor layer may be a mixed film including two or more of aregion of a CAAC-OS, a region of a polycrystalline oxide semiconductor,a region of an nc-OS, a region of an a-like OS, and a region of anamorphous oxide semiconductor. The mixed film has, for example, asingle-layer structure or a stacked-layer structure including two ormore of the above regions in some cases.

<Composition of CAC-OS>

Described below is the composition of a cloud-aligned composite oxidesemiconductor (CAC-OS) applicable to a transistor disclosed in oneembodiment of the present invention.

The CAC-OS has, for example, a composition in which elements included ina metal oxide are unevenly distributed. Materials including unevenlydistributed elements each have a size of greater than or equal to 0.5 nmand less than or equal to 10 nm, preferably greater than or equal to 1nm and less than or equal to 2 nm, or a similar size. Note that in thefollowing description of a metal oxide, a state in which one or moremetal elements are unevenly distributed and regions including the metalelement(s) are mixed is referred to as a mosaic pattern or a patch-likepattern. The regions each have a size of greater than or equal to 0.5 nmand less than or equal to 10 nm, preferably greater than or equal to 1nm and less than or equal to 2 nm, or a similar size.

Note that a metal oxide preferably contains at least indium. Inparticular, indium and zinc are preferably contained. In addition,aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, silicon,titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum,cerium, neodymium, hafnium, tantalum, tungsten, magnesium, and the likemay be contained.

For example, of the CAC-OS, an In—Ga—Zn oxide with the CAC composition(such an In—Ga—Zn oxide may be particularly referred to as CAC-IGZO) hasa composition in which materials are separated into indium oxide(InO_(X1), where X1 is a real number greater than 0) or indium zincoxide (In_(X2)Zn_(Y2)O_(Z2), where X2, Y2, and Z2 are real numbersgreater than 0), and gallium oxide (GaO_(X3), where X3 is a real numbergreater than 0) or gallium zinc oxide (Ga_(X4)Zn_(Y4)O_(Z4), where X4,Y4, and Z4 are real numbers greater than 0), and a mosaic pattern isformed. Then, InO_(X1) or In_(X2)Zn_(Y2)O_(Z2) forming the mosaicpattern is evenly distributed in the film. This composition is alsoreferred to as a cloud-like composition.

That is, the CAC-OS is a composite metal oxide with a composition inwhich a region including GaO as a main component and a region includingIn_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component are mixed. Notethat in this specification, for example, when the atomic ratio of In toan element M in a first region is greater than the atomic ratio of In toan element M in a second region, the first region has higher Inconcentration than the second region.

Note that a compound including In, Ga, Zn, and O is also known as IGZO.Typical examples of IGZO include a crystalline compound represented byInGaO₃(ZnO)_(m1) (m1 is a natural number) and a crystalline compoundrepresented by In_((i+x0))Ga_((1−x0))O₃(ZnO)_(m0) (−1≤x0≤1; m0 is agiven number).

The above crystalline compounds have a single-crystal structure, apolycrystalline structure, or a CAAC structure. Note that the CAACstructure is a crystal structure in which a plurality of IGZOnanocrystals have c-axis alignment and are connected in the a-b planedirection without alignment.

On the other hand, the CAC-OS relates to the material composition of ametal oxide. In a material composition of a CAC-OS including In, Ga, Zn,and O, nanoparticle regions including Ga as a main component areobserved in part of the CAC-OS and nanoparticle regions including In asa main component are observed in part thereof. These nanoparticleregions are randomly dispersed to form a mosaic pattern. Therefore, thecrystal structure is a secondary element for the CAC-OS.

Note that in the CAC-OS, a stacked-layer structure including two or morefilms with different atomic ratios is not included. For example, atwo-layer structure of a film including In as a main component and afilm including Ga as a main component is not included.

A boundary between the region including GaO_(X3) as a main component andthe region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a maincomponent is not clearly observed in some cases.

In the case where one or more of aluminum, yttrium, copper, vanadium,beryllium, boron, silicon, titanium, iron, nickel, germanium, zirconium,molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten,magnesium, and the like are contained instead of gallium in a CAC-OS,nanoparticle regions including the selected metal element(s) as a maincomponent(s) are observed in part of the CAC-OS and nanoparticle regionsincluding In as a main component are observed in part thereof, and thesenanoparticle regions are randomly dispersed to form a mosaic pattern inthe CAC-OS.

The CAC-OS can be formed by a sputtering method under conditions whereintentional substrate heating is not performed, for example. In the caseof forming the CAC-OS by a sputtering method, one or more selected froman inert gas (typically, argon), an oxygen gas, and a nitrogen gas maybe used as a deposition gas. The ratio of the flow rate of an oxygen gasto the total flow rate of the deposition gas at the time of depositionis preferably as low as possible, and for example, the flow ratio of anoxygen gas is preferably higher than or equal to 0% and less than 30%,further preferably higher than or equal to 0% and less than or equal to10%.

The CAC-OS is characterized in that no clear peak is observed inmeasurement using θ/2θ scan by an out-of-plane method, which is an X-raydiffraction (XRD) measurement method. That is, X-ray diffraction showsno alignment in the a-b plane direction and the c-axis direction in ameasured region.

In an electron diffraction pattern of the CAC-OS which is obtained byirradiation with an electron beam with a probe diameter of 1 nm (alsoreferred to as a nanometer-sized electron beam), a ring-like region withhigh luminance and a plurality of bright spots in the ring-like regionare observed. Therefore, the electron diffraction pattern indicates thatthe crystal structure of the CAC-OS includes a nanocrystal (nc)structure with no alignment in plan-view and cross-sectional directions.

For example, an energy dispersive X-ray spectroscopy (EDX) mapping imageconfirms that an In—Ga—Zn oxide with the CAC composition has a structurein which a region including GaO_(X3) as a main component and a regionincluding In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component areunevenly distributed and mixed.

The CAC-OS has a structure different from that of an IGZO compound inwhich metal elements are evenly distributed, and has characteristicsdifferent from those of the IGZO compound. That is, in the CAC-OS,regions including GaO₃ or the like as a main component and regionsincluding In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component areseparated to form a mosaic pattern.

The conductivity of a region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1)as a main component is higher than that of a region including GaO_(X3)or the like as a main component. In other words, when carriers flowthrough regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a maincomponent, the conductivity of a metal oxide is exhibited. Accordingly,when regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a maincomponent are distributed in a metal oxide like a cloud, highfield-effect mobility (μ) can be achieved.

In contrast, the insulating property of a region including GaO_(X3) orthe like as a main component is higher than that of a region includingIn_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component. In other words,when regions including GaO_(X3) or the like as a main component aredistributed in a metal oxide, a leakage current can be suppressed andfavorable switching operation can be achieved.

Accordingly, when a CAC-OS is used for a semiconductor element, theinsulating property derived from GaO_(X3) or the like and theconductivity derived from In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) complementeach other, whereby a high on-state current (I_(on)) and highfield-effect mobility (μ) can be achieved.

A semiconductor element including a CAC-OS has high reliability. Thus,the CAC-OS is suitably used in a variety of semiconductor devicestypified by a display.

Since a transistor including a CAC-OS in a semiconductor layer has highfield-effect mobility and high driving capability, the use of thetransistor in a driver circuit, a typical example of which is a scanline driver circuit that generates a gate signal, allows a displaydevice to have a narrow bezel. Furthermore, the use of the transistor ina signal line driver circuit (particularly in a demultiplexer connectedto an output terminal of a shift register included in a signal linedriver circuit) in a display device can reduce the number of wiringsconnected to the display device.

Furthermore, unlike a transistor including low-temperature polysilicon,the transistor including a CAC-OS in the semiconductor layer does notneed a laser crystallization step. Thus, the manufacturing cost of adisplay device can be reduced, even when the display device is formedusing a large substrate. In addition, the transistor including a CAC-OSin the semiconductor layer is preferably used for a driver circuit and adisplay portion in a large display device having high resolution such asultra high definition (“4K resolution”, “4K2K”, and “4K”) or super highdefinition (“8K resolution”, “8K4K”, and “8K”), in which case writingcan be performed in a short time and display defects can be reduced.

Alternatively, silicon may be used as a semiconductor in which a channelof a transistor is formed. Silicon may be amorphous silicon but ispreferably silicon having crystallinity, such as microcrystallinesilicon, polycrystalline silicon, or single-crystal silicon. Inparticular, polycrystalline silicon can be formed at a lower temperaturethan single-crystal silicon and has higher field-effect mobility andhigher reliability than amorphous silicon.

The bottom-gate transistor described in this embodiment is preferablebecause the use of the bottom-gate transistor can reduce the number ofmanufacturing steps. When amorphous silicon, which can be formed at alower temperature than polycrystalline silicon, is used for thesemiconductor layer, materials with low heat resistance can be used fora wiring, an electrode, or a substrate below the semiconductor layer,resulting in wider choice of materials. For example, an extremely largeglass substrate can be favorably used. Meanwhile, the top-gatetransistor is preferable because an impurity region is easily formed ina self-aligned manner in the top-gate transistor and variation incharacteristics can be reduced. The top-gate transistor is preferable incase of using polycrystalline silicon, single-crystal silicon, or thelike.

[Conductive Layer]

Examples of materials that can be used for a gate, a source, and a drainof a light-blocking transistor and for a conductive layer serving as awiring or an electrode included in a display device include a metal suchas aluminum, titanium, chromium, nickel, copper, yttrium, zirconium,molybdenum, silver, tantalum, or tungsten and an alloy containing any ofthese metals as its main component. A single-layer structure orstacked-layer structure including a film containing any of thesematerials can be used. For example, the following structures can beused: a single-layer structure of an aluminum film containing silicon, atwo-layer structure in which an aluminum film is stacked over a titaniumfilm, a two-layer structure in which an aluminum film is stacked over atungsten film, a two-layer structure in which a copper film is stackedover a copper-magnesium-aluminum alloy film, a two-layer structure inwhich a copper film is stacked over a titanium film, a two-layerstructure in which a copper film is stacked over a tungsten film, athree-layer structure in which a titanium film or a titanium nitridefilm, an aluminum film or a copper film, and a titanium film or atitanium nitride film are stacked in this order, and a three-layerstructure in which a molybdenum film or a molybdenum nitride film, analuminum film or a copper film, and a molybdenum film or a molybdenumnitride film are stacked in this order. Note that an oxide such asindium oxide, tin oxide, or zinc oxide may be used. Copper containingmanganese is preferably used because controllability of shape processingby etching is increased.

Examples of materials that can be used for a gate, a source, and a drainof a light-transmitting transistor and for a conductive layer serving asa wiring or an electrode in a display device include a conductive oxidesuch as indium oxide, indium tin oxide, indium zinc oxide, zinc oxide,or zinc oxide to which gallium is added, and graphene. It is alsopossible to use a metal material such as gold, silver, platinum,magnesium, nickel, tungsten, chromium, molybdenum, iron, cobalt, copper,palladium, or titanium; an alloy material containing any of these metalmaterials; or a nitride of any of these metal materials (e.g., titaniumnitride). In the case of using the metal material or the alloy material(or the nitride thereof), the film thickness is set small enough totransmit light. Alternatively, a stacked-layer film of any of the abovematerials can be used for the conductive layers. For example, astacked-layer film of indium tin oxide and an alloy of silver andmagnesium is preferably used because such a film can increase theconductivity. They can also be used for conductive layers for a varietyof wirings and electrodes included in a display device, and conductivelayers (e.g., conductive layers serving as a pixel electrode and acommon electrode) included in a display element.

As a light-transmitting conductive material, an oxide semiconductorwhose resistance is reduced by, for example, introduction of an impurityelement (such an oxide semiconductor is referred to as an oxideconductor or OC) is preferably used.

[Insulating Layer]

Examples of an insulating material that can be used for the insulatinglayers include a resin such as acrylic or epoxy resin, a resin having asiloxane bond, and an inorganic insulating material such as siliconoxide, silicon oxynitride, silicon nitride oxide, silicon nitride, oraluminum oxide.

The light-emitting element is preferably provided between a pair ofinsulating films with low water permeability, in which case impuritiessuch as water can be prevented from entering the light-emitting element.Thus, a decrease in device reliability can be prevented.

Examples of the insulating film with low water permeability include afilm containing nitrogen and silicon (e.g., a silicon nitride film and asilicon nitride oxide film) and a film containing nitrogen and aluminum(e.g., an aluminum nitride film). Alternatively, a silicon oxide film, asilicon oxynitride film, an aluminum oxide film, or the like may beused.

For example, the moisture vapor transmission rate of the insulating filmwith low water permeability is lower than or equal to 1×10⁻⁵[g/(m²·day)], preferably lower than or equal to 1×10⁻⁶ [g/(m²·day)],further preferably lower than or equal to 1×10⁻⁷ [g/(m²·day)], stillfurther preferably lower than or equal to 1×10⁻⁸ [g/(m²·day)].

[Liquid Crystal Element]

The liquid crystal element can employ, for example, a vertical alignment(VA) mode. Examples of the vertical alignment mode include amulti-domain vertical alignment (MVA) mode, a patterned verticalalignment (PVA) mode, and an advanced super view (ASV) mode.

The liquid crystal element can employ a variety of modes. For example,instead of a VA mode, a liquid crystal element can employ a twistednematic (TN) mode, an in-plane switching (IPS) mode, a fringe fieldswitching (FFS) mode, an axially symmetric aligned micro-cell (ASM)mode, an optically compensated birefringence (OCB) mode, a ferroelectricliquid crystal (FLC) mode, an antiferroelectric liquid crystal (AFLC)mode, an electrically controlled birefringence (ECB) mode, or aguest-host mode.

The liquid crystal element controls transmission or non-transmission oflight utilizing an optical modulation action of liquid crystal. Theoptical modulation action of liquid crystal is controlled by an electricfield applied to the liquid crystal (including a horizontal electricfield, a vertical electric field, and an oblique electric field). As theliquid crystal used for the liquid crystal element, thermotropic liquidcrystal, low-molecular liquid crystal, high-molecular liquid crystal,polymer dispersed liquid crystal (PDLC), polymer network liquid crystal(PNLC), ferroelectric liquid crystal, anti-ferroelectric liquid crystal,or the like can be used. Such a liquid crystal material exhibits acholesteric phase, a smectic phase, a cubic phase, a chiral nematicphase, an isotropic phase, or the like depending on conditions.

As the liquid crystal material, either of a positive liquid crystal anda negative liquid crystal may be used, and an appropriate liquid crystalmaterial may be used depending on the mode or design to be used.

An alignment film can be provided to adjust the alignment of a liquidcrystal. In the case where a horizontal electric field mode is employed,a liquid crystal exhibiting a blue phase for which an alignment film isunnecessary may be used. A blue phase is one of liquid crystal phases,which is generated just before a cholesteric phase changes into anisotropic phase while temperature of cholesteric liquid crystal isincreased. Since the blue phase appears only in a narrow temperaturerange, a liquid crystal composition in which a chiral material is mixedto account for several weight percent or more is used for the liquidcrystal layer in order to improve the temperature range. The liquidcrystal composition which includes liquid crystal exhibiting a bluephase and a chiral material has a short response time and opticalisotropy, which makes the alignment process unneeded. In addition, theliquid crystal composition which includes liquid crystal exhibiting ablue phase and a chiral material has a small viewing angle dependence.An alignment film does not need to be provided and rubbing treatment isthus not necessary; accordingly, electrostatic discharge damage causedby the rubbing treatment can be prevented and defects and damage of theliquid crystal display device in the manufacturing process can bereduced.

As the liquid crystal element, a transmissive liquid crystal element, areflective liquid crystal element, a semi-transmissive liquid crystalelement, or the like can be used.

In one embodiment of the present invention, in particular, atransmissive liquid crystal element can be suitably used.

In the case where a transmissive or semi-transmissive liquid crystalelement is used, two polarizing plates are provided such that a pair ofsubstrates is sandwiched therebetween. Furthermore, a backlight isprovided on the outer side of the polarizing plate. As the backlight, adirect-below backlight or an edge-light backlight may be used. It ispreferable to use a direct-below backlight including an LED to performlocal dimming easily and increase the contrast. It is preferable to usean edge-light backlight to reduce the thickness of a module includingthe backlight.

When an edge-light type backlight is off, see-through display can beperformed.

[Light-Emitting Element]

As the light-emitting element, a self-luminous element can be used, andan element whose luminance is controlled by current or voltage isincluded in the category of the light-emitting element. For example, anLED, an organic EL element, an inorganic EL element, or the like can beused.

The light-emitting element has a top-emission structure, abottom-emission structure, a dual-emission structure, or the like. Aconductive film that transmits visible light is used as the electrodethrough which light is extracted. A conductive film that reflectsvisible light is preferably used as the electrode through which no lightis extracted.

In one embodiment of the present invention, a top-emission ordual-emission light emitting element can be particularly preferablyused.

The EL layer includes at least a light-emitting layer. In addition tothe light-emitting layer, the EL layer may further include one or morelayers containing any of a substance with a high hole-injectionproperty, a substance with a high hole-transport property, ahole-blocking material, a substance with a high electron-transportproperty, a substance with a high electron-injection property, asubstance with a bipolar property (a substance with a high electron- andhole-transport property), and the like.

For the EL layer, a low-molecular compound or a high-molecular compoundcan be used, and an inorganic compound may also be used. Each of thelayers included in the EL layer can be formed by any of the followingmethods: an evaporation method (including a vacuum evaporation method),a transfer method, a printing method, an inkjet method, a coatingmethod, and the like.

When a voltage higher than the threshold voltage of the light-emittingelement is applied between a cathode and an anode, holes are injected tothe EL layer from the anode side and electrons are injected to the ELlayer from the cathode side. The injected electrons and holes arerecombined in the EL layer and a light-emitting substance contained inthe EL layer emits light.

In the case where a light-emitting element emitting white light is usedas the light-emitting element, the EL layer preferably contains two ormore kinds of light-emitting substances. For example, the two or morekinds of light-emitting substances are selected so as to emit light ofcomplementary colors to obtain white light emission. Specifically, it ispreferable to contain two or more selected from light-emittingsubstances emitting light of red (R), green (G), blue (B), yellow (Y),orange (O), and the like and light-emitting substances emitting lightcontaining two or more of spectral components of R, G, and B. Thelight-emitting element preferably emits light with a spectrum having twoor more peaks in the wavelength range of a visible light region (e.g.,350 nm to 750 nm). An emission spectrum of a material that emits lighthaving a peak in a yellow wavelength range preferably includes spectralcomponents also in green and red wavelength ranges.

Preferably, a light-emitting layer containing a light-emitting materialemitting light of one color and a light-emitting layer containing alight-emitting material emitting light of another color are stacked inthe EL layer. For example, the plurality of light-emitting layers in theEL layer may be stacked in contact with each other or may be stackedwith a region not including any light-emitting material therebetween.For example, between a fluorescent layer and a phosphorescent layer, aregion that contains the same material as the fluorescent layer orphosphorescent layer (for example, a host material or an assistmaterial) and no light-emitting material may be provided. Thisfacilitates the manufacture of the light-emitting element and reducesthe drive voltage.

The light-emitting element may be a single element including one ELlayer or a tandem element in which a plurality of EL layers are stackedwith a charge generation layer therebetween.

The conductive film that transmits visible light can be formed using,for example, indium oxide, indium tin oxide, indium zinc oxide, zincoxide, or zinc oxide to which gallium is added. Alternatively, a film ofa metal material such as gold, silver, platinum, magnesium, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, ortitanium; an alloy containing any of these metal materials; or a nitrideof any of these metal materials (e.g., titanium nitride) formed thinenough to have a light-transmitting property can be used. Alternatively,a stacked-layer film of any of the above materials can be used for theconductive layers. For example, a stacked-layer film of indium tin oxideand an alloy of silver and magnesium is preferably used, in which caseconductivity can be increased. Further alternatively, graphene or thelike may be used.

For the conductive film that reflects visible light, for example, ametal material such as aluminum, gold, platinum, silver, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, or palladium or analloy containing any of these metal materials can be used. Lanthanum,neodymium, germanium, or the like may be added to the metal material orthe alloy. Alternatively, an alloy containing aluminum (an aluminumalloy) such as an alloy of aluminum and titanium, an alloy of aluminumand nickel, or an alloy of aluminum and neodymium may be used.Alternatively, an alloy containing silver such as an alloy of silver andcopper, an alloy of silver and palladium, or an alloy of silver andmagnesium may be used. An alloy containing silver and copper ispreferable because of its high heat resistance. Furthermore, when ametal film or a metal oxide film is stacked in contact with an aluminumfilm or an aluminum alloy film, oxidation can be suppressed. Examples ofa material for the metal film or the metal oxide film include titaniumand titanium oxide. Alternatively, the above conductive film thattransmits visible light and a film containing a metal material may bestacked. For example, a stack of silver and indium tin oxide, a stack ofan alloy of silver and magnesium and indium tin oxide, or the like canbe used.

Each of the electrodes can be formed by an evaporation method or asputtering method. Alternatively, a discharging method such as an inkjetmethod, a printing method such as a screen printing method, or a platingmethod may be used.

Note that the aforementioned light-emitting layer and layers containinga substance with a high hole-injection property, a substance with a highhole-transport property, a substance with a high electron-transportproperty, a substance with a high electron-injection property, asubstance with a bipolar property, and the like may include an inorganiccompound such as a quantum dot or a high molecular compound (e.g., anoligomer, a dendrimer, and a polymer). For example, used for thelight-emitting layer, the quantum dot can serve as a light-emittingmaterial.

The quantum dot may be a colloidal quantum dot, an alloyed quantum dot,a core-shell quantum dot, a core quantum dot, or the like. The quantumdot containing elements belonging to Groups 12 and 16, elementsbelonging to Groups 13 and 15, or elements belonging to Groups 14 and16, may be used. Alternatively, the quantum dot containing an elementsuch as cadmium, selenium, zinc, sulfur, phosphorus, indium, tellurium,lead, gallium, arsenic, or aluminum may be used.

[Adhesive Layer]

As the adhesive layer, a variety of curable adhesives, e.g., aphotocurable adhesive such as an ultraviolet curable adhesive, areactive curable adhesive, a thermosetting adhesive, and an anaerobicadhesive can be used. Examples of these adhesives include an epoxyresin, an acrylic resin, a silicone resin, a phenol resin, a polyimideresin, an imide resin, a polyvinyl chloride (PVC) resin, a polyvinylbutyral (PVB) resin, an ethylene vinyl acetate (EVA) resin, and thelike. In particular, a material with low moisture permeability, such asan epoxy resin, is preferred. Alternatively, a two-component resin maybe used. Still alternatively, an adhesive sheet or the like may be used.

Furthermore, the resin may include a drying agent. For example, asubstance that adsorbs moisture by chemical adsorption, such as oxide ofan alkaline earth metal (e.g., calcium oxide or barium oxide), can beused. Alternatively, a substance that adsorbs moisture by physicaladsorption, such as zeolite or silica gel, may be used. The drying agentis preferably included because it can prevent impurities such asmoisture from entering the element, thereby improving the reliability ofthe display panel.

In addition, it is preferable to mix a filler with a high refractiveindex or light-scattering member into the resin, in which case lightextraction efficiency can be enhanced. For example, titanium oxide,barium oxide, zeolite, zirconium, or the like can be used.

[Connection Layer]

As the connection layers, an anisotropic conductive film (ACF), ananisotropic conductive paste (ACP), or the like can be used.

[Coloring Layer]

As examples of a material that can be used for the coloring layers, ametal material, a resin material, and a resin material containing apigment or dye can be given.

[Light-Blocking Layer]

Examples of a material that can be used for the light-blocking layerinclude carbon black, titanium black, a metal, a metal oxide, and acomposite oxide containing a solid solution of a plurality of metaloxides. The light-blocking layer may be a film containing a resinmaterial or a thin film of an inorganic material such as a metal. Astacked-layer film containing the material of the coloring layer canalso be used for the light-blocking layer. For example, a stacked-layerstructure of a film containing a material of a coloring layer whichtransmits light of a certain color and a film containing a material of acoloring layer which transmits light of another color can be employed.The coloring layer and the light-blocking layer are preferably formedusing the same material, in which case the same manufacturing apparatuscan be used and the process can be simplified.

The above is the description of each of the components.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Example 1

In this example, a transistor was formed with materials that transmitvisible light.

[Structure of Transistor] The structure of the formed transistor isshown in FIG. 21A. The formed transistor was a bottom-gate transistor.The formed transistor was a visible-light-transmitting transistor inwhich a semiconductor layer (OS), a first gate electrode (Bottom-gateelectrode), a second gate electrode (Back-gate electrode), and a sourceelectrode and a drain electrode (S/D electrode) includedlight-transmitting materials.

[Formation of Transistor]

A method for forming the transistor is described below. For the firstgate electrode, an indium tin oxide film containing silicon was formedby a sputtering method. Next, for a wiring to be a gate line (notillustrated), a copper film was formed by a sputtering method. For agate insulating film (GI), a stack of a silicon nitride film and asilicon oxide film was formed by a plasma CVD method. For thesemiconductor layer, an In—Ga—Zn oxide film was formed by a sputteringmethod. For the source electrode and the drain electrode, an indium zincoxide film was formed by a sputtering method. In processing into thesource electrode and the drain electrode, an etchant different from thatused for processing into the semiconductor layer was used to preventremoval of the semiconductor layer. Then, for a wiring to be a sourceline (not illustrated), a copper film was formed by a sputtering method.Next, for an insulating layer (Passivation layer), a silicon oxidenitride film was formed by a plasma CVD method. Then, the second gateelectrode was formed.

As the semiconductor layer, a stack of a CAC-OS film and a CAAC-OS filmwas used. The CAAC-OS film, having high chemical and plasma resistance,was formed on the upper side, thereby reducing the influence of damagein formation of the transistor. As the second gate electrode, a stack ofa CAAC-OS film and a CAC-OS film was used.

[Electrical Characteristics of Transistor]

FIG. 21B shows measurement results of electrical characteristics of theformed transistor. The source-drain currents (Id) were measured atdifferent gate-source voltages (Vg) (i.e., Id-Vg characteristics weremeasured). The drain voltages (Vd) were set to 0.1 V and 20 V. FIG. 21Balso shows field-effect mobility estimated from the Id-Vgcharacteristics at Vd of 20 V. The channel length and the channel widthof the measured transistor were approximately 2 μm and approximately3.25 μm, respectively. As shown in FIG. 21B, the transistor was normallyoff and had favorable characteristics even with the extremely smallchannel length. The formed transistor had field-effect mobility over 35cm²/Vs, while a transistor in a commercial product had a field-effectmobility of approximately 10 cm²/Vs.

FIG. 22 shows measurement results of the sheet resistances of an oxideconductor film (OC), an indium zinc oxide film (IZO: registeredtrademark), and an indium tin oxide film containing silicon (ITSO),which were used as the light-transmitting conductive films in the formedtransistor. As shown in the graph, each of them had sufficiently lowresistance.

The above is the description of Example 1. At least part of this examplecan be implemented in combination with any of the other embodiments andthe other examples described in this specification as appropriate.

Example 2

In this example, a display device of one embodiment of the presentinvention was formed. Here, a display device with a light-emittingelement and a liquid crystal element capable of switching between the VRmode and the AR mode was formed.

[Light-Emitting Element]

The light-emitting element included in the display device is describedhere. FIG. 23 shows the structure of the light-emitting element. Thelight-emitting element had a pair of electrodes each of which included atransparent conductive film so that the light-emitting element served aspart of the transmission region to improve the transmittance in thetransmission mode. The light-emitting element employed a two-layertandem structure in which a blue light-emitting layer and a red andgreen light-emitting layer were stacked with an intermediate layertherebetween. The blue light-emitting layer contained a fluorescentmaterial, and the red and green light-emitting layer contained aphosphorescent material.

[Liquid Crystal Element]

The liquid crystal element served as a shutter for switching between theAR mode and the VR mode. The liquid crystal element blocked externallight in VR mode and transmitted external light in AR mode. Thus,passive driving, using a simple structure without a transistor or thelike, was employed. Since no light-blocking material was needed forelectrodes and the like of the liquid crystal element, the apertureratio was 100%.

When the display device is used mainly in VR mode, the use of a normallyblack liquid crystal element can reduce power consumption. In thisexample, a VA mode liquid crystal element was employed. In forming a VAmode passive matrix liquid crystal element, optical alignment treatmentwas performed. Accordingly, liquid crystal molecules were capable ofbeing aligned in the same direction across the whole liquid crystalelement to which a voltage was applied; thus, the transmittance in ARmode was heightened.

FIG. 24 shows the voltage-transmittance characteristics of the formedliquid crystal element. As shown, the liquid crystal element hadnormally black characteristics with extremely low transmittance when notapplied with a voltage.

[Formation of Display Device]

A method for manufacturing a display device including a light-emittingelement and a liquid crystal element between a pair of substrates isdescribed below. FIGS. 25A to 25F are schematic views illustrating amanufacturing process.

As shown in FIG. 25A, first, a separation layer (Separation Layer), aninsulating layer (Passivation Layer), a control circuit including atransistor and the like (Control Circuit) were formed in this order overa glass substrate (Glass). A color filter (CF) was formed over anotherglass substrate. To improve the transmittance in the transmission mode,no black matrix was formed. Next, as shown in FIG. 25B, a light-emittingelement (OLED) was formed over the control circuit, and the two glasssubstrates were attached to each other with a sealing resin. Then, asshown in FIG. 25C, separation was performed between the separation layerand the insulating layer. After that, as shown in FIG. 25D, atransparent conductive film (ITO) serving as one electrode of the liquidcrystal element was formed over the insulating layer. Subsequently, atransparent conductive film serving as the other electrode of the liquidcrystal element was similarly formed over another glass substrate. Asshown in FIG. 25E, the two glass substrates were attached to each otherwith liquid crystal (LC) therebetween. In this way, a thin displaydevice in which the light-emitting element, the control circuit, and theliquid crystal element were between the two glass substrates wasobtained. Finally, as shown in FIG. 25F, the glass substrates werepartly cut so that a terminal portion was exposed.

Table 1 shows the specifications of the formed display device, and Table2 shows the specifications of the liquid crystal element. A zigzagarrangement shown in FIGS. 6A to 6D was employed for the pixelstructure, and the display device had an extremely high definition of1,058 ppi.

TABLE 1 Specifications Screen Diagonal 2.78 inches Driving Method ActiveMatrix Resolution 2560 × RGB × 1440 (WQHD) Pixel Density 1058 ppi PixelPitch 24 μm × 24 μm (approx.) Aperture ratio (OLED) 10.8% Effectivetransmission 66.1% area ratio Pixel Arrangement zigzag Coloring MethodWhite Tandem OLED + Color Filter Pixel Circuit 2Tr + 1C/pixel SourceDriver COF + Demultiplexer Scan Driver Integrated Emission Type DualEmission

TABLE 2 Specifications Screen Diagonal 3.26 inches Driving MethodPassive LC VA mode

[Measurement of Transmittance]

To confirm that the transmittance of a display device in thetransmission mode would increase by the use of a transparent pixelincluding visible-light-transmitting conductive films for conductivelayers other than a bus line of the display device, the following twosamples were formed and the transmittances thereof were measured.

In each of the samples, a control circuit was formed over a glasssubstrate, and sealed by another glass substrate with a sealing resin.Thus, each of the samples included no light-emitting element and noliquid crystal element. One of the samples includedvisible-light-transmitting conductive films for conductive layers otherthan a bus line and had a transparent pixel. The other of the samplesincluded visible-light-blocking conductive films also for conductivelayers other than a bus line.

As shown in FIG. 26A, intensity I₁ of light transmitted through each ofthe samples was measured. Transmittance T was a value obtained bydividing the transmission light intensity I₁ by incident light intensityI₀.

FIGS. 26B and 26C show the measured transmittance of the sample with thetransparent pixel (Sample) and that of the sample without a transparentpixel (Reference). FIG. 26B shows the measurement results of thetransmittance in a straight direction, and FIG. 26C shows themeasurement results of the transmittance in all directions with anintegrating sphere. In each of FIGS. 26B and 26C, the horizontal axisrepresents wavelength and the vertical axis represents transmittance. Asshown in FIG. 26B, while the transmittance of the sample without atransparent pixel was approximately 7%, the transmittance of the samplewith the transparent pixel reached approximately 30%. As in FIG. 26Cshowing the measurement results in all directions, while the samplewithout a transparent pixel had a transmittance of approximately 20%,the sample with the transparent pixel had an improved transmittance ofapproximately 48% on average. As shown, the use of the transparent pixelincreased the transmittance.

[Display Device 1]

A display panel with extremely high definition was formed with atransparent pixel. The display panel formed here included no liquidcrystal element, and the specifications of the display panel were thesame as those in Table 1.

FIG. 27 is a photograph of the display panel including the transparentpixel that was in the display state. This display panel did not includea liquid crystal element but included a control circuit, alight-emitting element, and a color filter that were sealed between apair of substrates. FIG. 27 shows that the display panel with thetransparent pixel operated normally.

[Display Device 2]

A display panel that included a light-emitting element and a liquidcrystal element between a pair of substrates and was capable ofswitching between the VR mode and the AR mode was formed. This displaypanel included a pixel including a light-blocking conductive film, not atransparent pixel.

FIG. 28A is a photograph of the display panel displaying an image in VRmode, and FIG. 28C is a photograph of the display panel displaying animage in AR mode. FIGS. 28B and 28D are schematic views showing thesituation in photographing. The formed display panel was positioned overthe screen of a smartphone displaying a background image, and thephotograph of the formed display panel was taken from the top surfaceside.

In VR mode, the background image was not seen because the liquid crystalelement was in the light-blocking state; thus, an image displayed onlywith the light-emitting element was seen. In contrast, in AR mode, theimage displayed with the light-emitting element was superimposed on thebackground image transmitted through the display panel.

The display panel shown here included no transparent pixel. When atransparent pixel is used instead, the transmission image can be seenmore clearly.

The above is the description of Example 2. At least part of this examplecan be implemented in combination with any of the other embodiments andthe other examples described in this specification as appropriate.

Example 3

An optical system including the display device formed in Example 2 isdescribed here.

FIG. 29A is a schematic diagram of an optical system (Optical System).The optical system included a pair of lenses (Lens) between which thedisplay panel (Hybrid Display) was sandwiched. A prism (Prism) forinverting an image was positioned opposite to an observer. The displaypanel was positioned at a focal point of the pair of lenses. For thepair of lenses, biconvex lenses with the same focal distance were used.

As the prism, a Schmidt-Pechan erect prism like one shown in FIG. 29Bwas used. Any erect prism can be used as the prism, and for example, anAbbe-Koenig prism may be used.

As shown in FIG. 29A, light entering the prism (the light is indicatedby a dashed line) was inverted by the prism, refracted by the firstlens, transmitted through the display panel, and inverted again whenrefracted by the second lens; accordingly, the observer was able to seean erected image.

FIG. 29A schematically shows a background image (Background image), adisplay image (display image) shown by the display panel, and a combinedimage (Superimposed image).

Image display was performed with the optical system shown in FIG. 29A.FIG. 29C is a photograph of the display panel displaying an image in VRmode, and FIG. 29D is a photograph of the display panel displaying animage in AR mode. As shown, the background image was observed clearly inAR mode, unaffected by diffraction due to the pixel periodicity of thedisplay panel. In addition, the combined image in which both thebackground image and the display image were erected was obtained.

The above is the description of Example 3.

REFERENCE NUMERALS

10: display device, 10 a: electronic device, 10EL: display portion,10LC: transmission control portion, 11: control portion, 12: opticalsensor, 13EL: driver portion, 13LC: driver portion, 15: arithmeticportion, 20B: light, 20 e: light, 20G: light, 20in: light, 20R: light,20 t: transmission light, 21: substrate, 22: display region, 23:conductive layer, 24: liquid crystal, 25: conductive layer, 30: pixel,31: substrate, 39 a: polarizing plate, 39 b: polarizing plate, 40:liquid crystal element, 41 a: pixel circuit, 41 b: pixel circuit, 42 a:pixel circuit, 42 b: pixel circuit, 43 a: pixel circuit, 43 b: pixelcircuit, 45: functional layer, 45 a: functional layer, 45 b: functionallayer, 50: subpixel, 50 a: subpixel, 51: wiring, 51 a: wiring, 51 b:wiring, 52: wiring, 52 a: wiring, 52 b: wiring, 52 c: wiring, 52 d:wiring, 53: wiring, 53 a: wiring, 53 b: wiring, 53 c: wiring, 55:semiconductor layer, 56: conductive layer, 57: conductive layer, 58:conductive layer, 59: wiring, 60: display element, 61: transistor, 61 a:transistor, 61 b: transistor, 61 c: transistor, 61 d: transistor, 62:transistor, 62 a: transistor, 63: capacitor, 64: pixel electrode, 70:pixel unit, 70 a: pixel, 70 b: pixel, 71 a: subpixel, 71 b: subpixel, 72a: subpixel, 72 b: subpixel, 73 a: subpixel, 73 b: subpixel, 81:insulating layer, 83: insulating layer, 84: insulating layer, 89:adhesive layer, 90: light-emitting element, 90B: light-emitting element,90G: light-emitting element, 90R: light-emitting element, 90W:light-emitting element, 91: conductive layer, 91B1: pixel electrode,91B2: pixel electrode, 91G1: pixel electrode, 91G2: pixel electrode,91R1: pixel electrode, 91R2: pixel electrode, 92: EL layer, 92B: ELlayer, 92G: EL layer, 92R: EL layer, 93: conductive layer, 100: imagedisplay device, 100 a: image display device, 101: housing, 102: displayportion, 102EL: display panel, 102 p: display panel, 103: camera, 104:mounting fixture, 117: insulating layer, 130 a: polarizing plate, 130 b:polarizing plate, 133 a: alignment film, 133 b: alignment film, 134:coloring layer, 161: adhesive layer, 162: adhesive layer, 191:conductive layer, 192: EL layer, 193: conductive layer, 194: insulatinglayer, 201: transistor, 202: transistor, 204: connection portion, 205:transistor, 206: transistor, 207: connection portion, 208: transistor,209: wiring, 211: insulating layer, 212: insulating layer, 213:insulating layer, 214: insulating layer, 215: insulating layer, 216:insulating layer, 217: insulating layer, 220: insulating layer, 221:conductive layer, 221 t: conductive layer, 222: conductive layer, 222 t:conductive layer, 223: conductive layer, 224: conductive layer, 231:semiconductor layer, 242: connection layer, 243: connector, 252:connection portion, 300: display panel, 311: conductive layer, 312:liquid crystal, 313: conductive layer, 340: liquid crystal element, 351:substrate, 351 a: substrate, 351 b: substrate, 352: adhesive layer, 360:light-emitting element, 361: substrate, 361 a: substrate, 361 b:substrate, 362: display portion, 364: circuit, 365: wiring, 366: touchsensor, 372: FPC, 373: IC.

This application is based on Japanese Patent Application Serial No.2016-219350 filed with Japan Patent Office on Nov. 10, 2016, JapanesePatent Application Serial No. 2016-233422 filed with Japan Patent Officeon Nov. 30, 2016, and Japanese Patent Application Serial No. 2017-099585filed with Japan Patent Office on May 19, 2017, the entire contents ofwhich are hereby incorporated by reference.

1. A display device comprising: a light-emitting element; a firsttransistor electrically connected to the light-emitting element; and aliquid crystal element overlapping with the first transistor, whereinthe first transistor includes a first gate electrode, a firstsemiconductor layer, a first source electrode, and a first drainelectrode, wherein at least one of the first gate electrode, the firstsemiconductor layer, the first source electrode, and the first drainelectrode is configured to transmit visible light, wherein thelight-emitting element includes a first electrode, a second electrode,and a light-emitting layer between the first electrode and the secondelectrode, wherein the first electrode and the second electrode are eachconfigured to transmit visible light, and wherein the liquid crystalelement transmits light when applied with an electric field, and blockslight when not applied with an electric field.
 2. The display deviceaccording to claim 1, wherein at least one of the first semiconductorlayer, the first gate electrode, the first source electrode, and thefirst drain electrode includes a metal oxide.
 3. The display deviceaccording to claim 1, further comprising: a second transistorelectrically connected to and overlapping with the liquid crystalelement, wherein the second transistor includes a second gate electrode,a second semiconductor layer, a second source electrode, and a seconddrain electrode, and wherein at least one of the second gate electrode,the second semiconductor layer, the second source electrode, and thesecond drain electrode is configured to transmit visible light.
 4. Thedisplay device according to claim 3, wherein the first transistor andthe second transistor are on the same plane.
 5. The display deviceaccording to claim 1, wherein the liquid crystal element is a passivematrix liquid crystal element or a segment liquid crystal element. 6.The display device according to claim 1, further comprising: a firstsubstrate; a second substrate; and an insulating layer; wherein theinsulating layer is between the first substrate and the secondsubstrate, wherein the light-emitting element is between the firstsubstrate and the insulating layer, wherein the liquid crystal elementis between the second substrate and the insulating layer, and wherein atleast one of the first gate electrode, the first semiconductor layer,the first source electrode, and the first drain electrode of the firsttransistor is in contact with the insulating layer.
 7. The displaydevice according to claim 6, further comprising: a wiring electricallyconnected to the liquid crystal element, wherein the first transistorand the wiring are between the insulating layer and the first substrate,and wherein the wiring is electrically connected to the liquid crystalelement in an opening in the insulating layer.
 8. The display deviceaccording to claim 7, further comprising a second transistorelectrically connected to the wiring.
 9. The display device according toclaim 7, wherein the wiring is configured to transmit visible light. 10.The display device according to claim 1, further comprising: a firstwiring; and a second wiring intersecting with the first wiring, whereinthe first wiring is electrically connected to the first gate electrodeof the first transistor, wherein the second wiring is electricallyconnected to one of the first source electrode and the first drainelectrode of the first transistor, and wherein the first wiring and thesecond wiring are each configured to block visible light.
 11. Thedisplay device according to claim 1, further comprising: a first wiring;and a second wiring intersecting with the first wiring, wherein thefirst wiring is electrically connected to the first gate electrode ofthe first transistor, wherein the second wiring is electricallyconnected to one of the first source electrode and the first drainelectrode of the first transistor, and wherein the first wiring and thesecond wiring are each configured to transmit visible light.
 12. Adisplay device comprising: a liquid crystal element; a first transistorover and overlapping with the liquid crystal element; a light-emittingelement over and electrically connected to the first transistor; and adisplay surface over the light-emitting element, wherein thelight-emitting element includes a first electrode, a second electrode,and a light-emitting layer between the first electrode and the secondelectrode, wherein the first electrode and the second electrode are eachconfigured to transmit visible light, and wherein the liquid crystalelement transmits light when applied with an electric field, and blockslight when not applied with an electric field.
 13. The display deviceaccording to claim 12, wherein the first transistor includes a firstgate electrode, a first semiconductor layer, a first source electrode,and a first drain electrode, and wherein at least one of the firstsemiconductor layer, the first gate electrode, the first sourceelectrode, and the first drain electrode is configured to transmitvisible light.
 14. The display device according to claim 12, wherein thefirst transistor includes a first gate electrode, a first semiconductorlayer, a first source electrode, and a first drain electrode, andwherein at least one of the first semiconductor layer, the first gateelectrode, the first source electrode, and the first drain electrodeincludes a metal oxide.
 15. The display device according to claim 12,further comprising: a second transistor electrically connected to andoverlapping with the liquid crystal element, wherein the secondtransistor includes a second gate electrode, a semiconductor layer, asecond source electrode, and a second drain electrode, and wherein atleast one of the second gate electrode, the semiconductor layer, thesecond source electrode, and the second drain electrode is configured totransmit visible light.
 16. The display device according to claim 15,wherein the first transistor and the second transistor are on the sameplane.
 17. The display device according to claim 12, wherein the liquidcrystal element is a passive matrix liquid crystal element or a segmentliquid crystal element.
 18. The display device according to claim 12,further comprising: a first substrate; a second substrate, and aninsulating layer; wherein the insulating layer is between the firstsubstrate and the second substrate, wherein the light-emitting elementis between the first substrate and the insulating layer, wherein theliquid crystal element is between the second substrate and theinsulating layer, wherein the first transistor includes a first gateelectrode, a first semiconductor layer, a first source electrode, and afirst drain electrode, and wherein at least one of the first gateelectrode, the first semiconductor layer, the first source electrode,and the first drain electrode of the first transistor is in contact withthe insulating layer.
 19. The display device according to claim 18,further comprising: a wiring electrically connected to the liquidcrystal element, wherein the first transistor and the wiring are betweenthe insulating layer and the first substrate, and wherein the wiring iselectrically connected to the liquid crystal element in an opening inthe insulating layer.
 20. The display device according to claim 19,further comprising a second transistor electrically connected to thewiring.
 21. The display device according to claim 19, wherein the wiringis configured to transmit visible light.
 22. The display deviceaccording to claim 12, further comprising: a first wiring; and a secondwiring intersecting with the first wiring, wherein the first transistorincludes a first gate electrode, a first semiconductor layer, a firstsource electrode, and a first drain electrode, wherein the first wiringis electrically connected to the first gate electrode of the firsttransistor, wherein the second wiring is electrically connected to oneof the first source electrode and the first drain electrode of the firsttransistor, and wherein the first wiring and the second wiring are eachconfigured to block visible light.
 23. The display device according toclaim 12, further comprising: a first wiring; and a second wiringintersecting with the first wiring, wherein the first transistorincludes a first gate electrode, a first semiconductor layer, a firstsource electrode, and a first drain electrode, wherein the first wiringis electrically connected to the first gate electrode of the firsttransistor, wherein the second wiring is electrically connected to oneof the first source electrode and the first drain electrode of the firsttransistor, and wherein the first wiring and the second wiring are eachconfigured to transmit visible light.